Daily highs/lows are always suspect on daily data. That's just the unfortunate reality. And it occurs over many data sources. Open/closes are generally fine. So you'll need to put your attention there in building a system. Not to worry. It can be done. And then you'll have greater confidence in the data.
You may want to check out algoseek.com. Their historical intraday is collected raw and provided "as is" from the exchanges.
%% That's why i like paper charts=less computer errors+ easier to correct paper charts. 10% or 20% errors dont happen that often,YAHOO has errors very frequently. QLD was off 50% one day/LOL but that was an ETF stock split/logical error/LOL
Some websites (Yahoo, SA, TradingView) have "fixed" the data and now show 719 as the high value, while Nasdaq still shows 872. I wonder what the logic is, if there is any logic...
When a trade takes place off the exchange (like between two funds) it is required to be reported by a certain time. I don't recall when but it is after the RTH. So it is reported to the exchange and it goes out as an out-of-sequence trade. The problem, for me and other backtesters, is that some data providers "correct" the daily regular-trading-hours data after the fact. Oh well. I just re-downloaded daily data from IQFeed. They have changed TSLAs high from 872 to 719. So sometime between after 10 PM on 3/1 and now 10 PM 3/3 they corrected their correction. I wonder if someone alerted them to the problem and they manually fixed it? I have seen the problem in data much older than two days where it is not fixed. Anyway, I was hoping for some information on how Polygon.io and ActiveTick handle the problem.