I was doing some backtesting and after getting some unreasonable gains, I looked into the details and found that Fidelity has not done price adjustment for a 1:10 split on Nov 26, 2019 for SNDE (See attachment for a chart of SNDE).

I did validation one time for many stocks if Fidelity was adjusting price for splits, and it was actually adjusting price for splits. So this looks like a miss.

I am looking at few options:
1. If this is one-off case, then I can ignore this one time and continue working with Fidelity's data. What is the experience of other users on this Forum - do you trust Fidelity's data and use it for your backtesting?
2. Explore some other data provider. What will be a reliable data provider for backtesting? I need only EOD data (no intraday data). Hopefully it can provide a way to take a snapshot of a past date (like what were the listed stocks on 7/4/2019 and what were the actual prices of the stocks on that day).

"Process a Stock Split ..." from the right-click (context) menu should rectify the missing split.

As to your #2, here's for your convenience: Map of Wealth-Lab Data Providers. Explore, pick whatever you like, study how they work, compare.

Thanks Eugene!

You're welcome.

Also, fixed the link in post #2.