It's interesting to look at 10 and 15 year performance of different mutual funds. If a fund has an impressive 10 and 15 year return (above average), but has struggle over the last three to five year period I look for reasons why. Sometimes it's a reason to stay away. Sometimes it's a reason to add to my watch list.
Energy/Natural Resource funds and also value tilted funds seem to be full of under performer right now.

Vanguard now reports YTD (10/29) of $1.75, StockCharts reports $1.73, and M* reports $1.75. That's more than yesterday's penny's worth of rounding error. While I appreciate that real investors care about real account balances, I consider the fund itself to be the authoritative source.
M* has a slider that can be used in the same way as with StockCharts. Curiously the StockCharts slider has one additional feature: the ability to enter explicitly the span of a timeframe, but not where that timeframe sits. M*, in contrast, provides the ability to input explicitly the beginning and end dates. I find that more valuable, as setting both dates automatically defines the span, while inputting the span does not determine the dates.
How would you get the total return of VWINX from 2/21/20 to 3/23/20?
The ability to show relative performance in a StockCharts graph is a cute little feature. It, like the ability to sort "historgrams" (more accurately called bar charts), presents an alternate visualization of data it has graphed.
StockCharts seems to carry a limited data set. When I ask PerfChart for "all" the data it has on VWINX, it only goes back to 1/4/1999. We all know that Wellesley is older than that. 1994 is an important down year to look at. It's just not there. M* provides the whole history back to 1970.
My personal bottom line is that I can live with almost any UI, but I can't live without accurate and complete data.

Key Points:
° Over the last 25 years, exceptionally outstanding fund performance nearly across the board was followed 5 years later by poor performance; this happened beginning in 2000, 2007, and 2014.
° When only a small number of funds excelled after the 2007-09 bear market, all were doing poorly by 5 years later.
° In early 2015, funds that were previously among the biggest performance winners suffered sharp dropoffs by 2020; the table below shows these funds and how badly they wound up doing.
° If these trends continue, the funds I list doing unusually well right now may not be your best choices for the next 5 years.
November Edition

When comparing performance, double-check the dates.
Charts may not have adjusted even if the dates may have scrolled. M* Performance tables have different dates for Day, Month, Quarter tabs.
M* Growth-of-10K uses a different methodology than that used by Stockcharts and Yahoo Finance. M* runs growth of 10K with reinvestment of distributions. Stockcharts and Yahoo Finance use adjusted-prices by making a ratio-adjustment for distributions; total-return is then found from current-price and the old adjusted-price. Stockcharts show both adjusted-prices [TICKER; default] and actual-prices [_TICKER].
I have done several comparisons and the results are close enough but may not match to the 2nd or 3rd decimal places. And then, M* Portfolio results don't exactly match with those from brokerage or fund statements after long times.
M* Premium allows Analyst Reports, X-Rays, longer Portfolios, Premium Screeners, Medalist features, some Premium articles/videos, etc. For most part, M* Basic is fine.

When I want to compare two funds in M*, I go to a legacy performance page for a fund, add other funds (one at a time), and get tabular comparisons. Not only how well each fund did over standardized periods, but how much better (or worse) the reference fund did than the other funds over the standardized periods.
For example, here's the legacy performance page for VWINX.
M* automatically provides a comparison with the fund category average and with a suitable benchmark. If I want to compare VWINX to another fund (or more) I click on "Compare" which opens a text input box. Then all I have to do is enter the fund ticker. No muss, no fuss, no need to click on a slider or link to retrieve data and generate comparisons for "all" standardized periods. Specifically, the tabular data automatically displayed includes:

1. Annual performance 2015-2019 and YTD (click on "Expanded view" for 2010 and up)
2. Trailing returns over the past 1 day, 1 week, 1 month, 3 month, 1, 3, 5, 10, and 15 years (computed to date, to end of last month, or to end of last quarter)
3. Monthly and quarterly returns over the past five years

Morningstar is designed for fund investors. StockCharts is designed for technical analysts (e.g. it defaults to price charts, not performance pages). As @Crash may have implied, M*'s new pages are, at least compared with its legacy pages, designed for no one.
That said, you found no inconsistencies. Check carefully the dates of the periods you were displaying. I'm not suggesting that the M* software is flawless, far from it. But the figures you read were correct for the dates on the graph. Lousy programming, but accurate data.
And none of this has anything to do with Premium features.

Hi @Old_Joe
I find this at Stockcharts for the two you mentioned. Placing a cursor at 9-30 date (on chart lines) shows a virtual tie for YTD at +4.12 and +4.13%.
You may also right click onto the slider below the chart (showing 210 days) and select 30 days for more recent actions.
The BAMBI choice did a bit better over their short life span, but took a bigger hit in March, versus the MINWAX fund. Sorry, the tickers reminded me of these proper names.
CHART

Looking at MNWAX at Schwab, I see a ytd return of -1.87% as of 9/30,but +3.58 as of 10/28.
With BAMBX, it's -0.04% and +3.41%, same dates.
What's the story on that?

Thanks. I am not as savvy as you, I expect, and have no idea if Fido is better than Schwab in this regard. I was surprised at being able to buy so 'visibly cheap' but have no idea if I could've bought it much cheaper and am therefore the ideal mark.
I am oldish for sure but hardly wise.
Only FD1k and truly low-lying / nearly invisible / modest types throw around millions, although this was close to half one.

What's a SPAC?

A special purpose acquisition company (SPAC) is a company with no commercial operations that is formed strictly to raise capital through an initial public offering (IPO) for the purpose of acquiring an existing company. Also known as "blank check companies," SPACs have been around for decades. In recent years, they've gone mainstream, attracting big-name underwriters and investors and raising a record amount of IPO money in 2019. In 2020, more than 50 SPACs have been formed in the U.S., as of the beginning of August, raising some $21.5 billion.

https://investopedia.com/terms/s/spac.asp
Investments in SPACs ETFs and BDCs:

You asked..."Does this have anything to do with M* Premium"?
You asked me if M* Basic was daily data. In order for me to answer the question I went to M* Interactive Charts to get detailed data. That lead me to find the inconsistencies and hence my question.
I can teach you how to use PerfCharts. Place your cursor over the slider and right click. This gives you several options including YTD which as of 10/29 shows +1.73%. Vanguard shows 1.75% as of 10/29.
Extra navigation is required in M* if you need to compare funds which is my main daily workload which is why Stockcharts is so much better for that purpose. They offer free Technical Analysis SharpCharts as well. They also offer nice seasonality charts which I seem to be using more frequently.

...think of this quote:

In the case of the corporate income tax, as the Harvard Business School’s Mihir Desai put it in an interview I recently did with him and his HBS colleague Bill George, “that tax is going to be borne by shareholders, workers, or customers.”

Interesting look at who pays corporate taxes:
who-pays-corporate-taxes-possibly-you

(1) Will Schwab honor TDA customers' grandfathered mutual fund commission rates of $15 for mutual funds like Primecap or Vanguard? I came into TDA as an old Waterhouse customer.
(2) Will Schwab allow monthly repeat purchases in these funds without transaction fees after the initial purchase (with a one-time commission)? This was something I liked about TDA.

In November 2019, Chuck Akre appeared on Wealthtrack (PBS and youtube) with his co-manager Neff and talked about the coming transition. I'm hanging on. Here's a link to that 25 minute program:
https://wealthtrack.com/finding-compounding-machines-with-the-great-investor-chuck-akre-his-gen-x-co-manager-john-neff/

We agree that StockCharts is wrong. Vanguard showed 1.71% (it now shows 1.75% through 10/29), and Vanguard is the authoritative source.
If you're clicking (interactive chart) and clicking again (YTD) at M* to get YTD data, it's not surprising that M* would appear less friendly than StockCharts. All you need do is read the (correct) YTD data straight from the fund's "home" page. No extra navigation required.
I don't see any easy way to get the same data out of StockCharts. I've found no instructions on how to query YTD performance data. I can only find StockChart instructions on how to input starting/ending dates for performance data.
https://support.stockcharts.com/doku.php?id=other-tools:perfcharts#changing_the_chart_s_time_period
The instructions say that one can use a slider to change dates, or one can hold the shift key (to adjust starting date) or hold the ctl key (to adjust ending date) and simultaneously click arrow keys until a date changes to the desired value.
[Sliders make lousy numeric input widgets. "Use a slider only when the precise value won’t matter to the user."
https://www.nngroup.com/articles/gui-slider-controls/]
At least once I get everything set up, and then I mouse over the chart, I do finally see the 1.70% figure you stated.
FWIW, here's an interactive M* chart with the correct 1.71% figure.
M* chart.
Does this have anything to do with M* premium features?

Click Interactive Chart...click YTD in top left under Add Comparison. Shows thru 10/28.
I see +1.34% in top right green for M*. We agree on Stockcharts +1.70%

For VWINX, I find M* performance, YTD at 1.71%; at Stockcharts = 1.70% at 5:40pm, Oct. 29.
NOTE: I'm using M* without an account/sign in. Never had a subscription.

I rarely use M* when I need detailed performance data. I found Stockcharts to be more user friendly and quicker, fund comparison easier and includes any distributions in the total return and quicker left click features. Something I always wondered... look at VWINX. Stockcharts YTD shows 1.7% thru 10/28, but M* Interactive YTD shows 1.34% thru 10/28. Where is the delta error?

Turnover for AKREX has always been very low, with M* pegging it a 4% currently. One consequence of this, I assume, is the amazing low tax bills presented to shareholders at year end. AUM have risen commensurate with the fund's great success since 2011, so management must have been faced with the problem of what to do with the new cash. Just what did Mr. Akre train the new colleagues to do if it was not to find new stocks for the fund to buy? Have they been trained to buy more of the winners? I enjoyed the anecdote about Mr. Akre's bedroom built off his office so he wouldn't have to stop working. OTOH, I have to wonder why a PM would need to work such long hours at a quintessential buy-and-hold fund. Seems as though he could go home and sleep peacefully. We have more than one account happily invested in AKREX.

M* Premium Fund Screener:
(Fund Category = Bear Market)
and (Distinct Portfolio Only = Yes)
and (Fund Name not like %ultra%)
and (Fund Name not like 2X)
and (Fund Name not like Inv)
That cuts the fund search down to a handful (5). Few enough to look at one by one.
Of course there's a more basic question of what "leveraged vehicles" you're expecting to exclude. For example, GRZZX "can invest in securities that may have a leveraging effect (such as derivatives and forward-settling securities) which may increase market exposure, magnify investment risks, and cause losses to be realized more quickly."
https://fundresearch.fidelity.com/mutual-funds/summary/527289797
Even if you don't consider that leveraged, what about BEARX? The fact that the top ten holdings amount to -177% of assets (from the M* screener) suggests that a look at the prospectus is in order.
"Under normal market conditions, the Fund will use leverage in implementing its investment strategies, and the aggregate exposure of the Fund's short positions plus its long positions is expected to exceed the Fund's net asset value." Summary Prospectus.

One simple example - get a quick comparison/filter of bond funds that made over 2.1% in 2013 (generally a down year for bonds).
The screen tells me that the main type of bonds that that did well was junk bonds: 39 bank loan funds, 139 HY bond funds, 5 core plus, 23 multi-sector, 16 nontraditional. There were also a few funds in less "junky" categories: 2 corporate bond funds, 1 EM local currency fund, 7 short term, and one word bond (hedged) fund.
Only 11 funds above junk (above BB), only 2 of those above BBB. Mostly "deep" junk.
Reset the filter to retrieve trailing returns between 0% and 2.1% exclusive, and one starts seeing lots of muni funds.
It used to be a lot easier to get info out of the screener before M* broke the ability to build custom views (which I had used to get 15 year trailing return data, among other things). It's still possible to coax all this info out from a screen, but one needs to do it via filters.