Let's say you're me, you have an idea about consistently buying Nasdaq 100 stocks that drop, based on the idea of people overreacting to news. So you use Wayback Machine to get old Nasdaq 100 lists, then pull the data from yfinance.
You'll see a lot of notifications that the ticker is expired, but let's say you plow through with your analysis anyway. Well, guess what, the strategy is going to be insanely biased towards success because whatever system you use isn't going to pick stocks that were delisted! In fact for 2000, out of the Nasdaq 100, only 32 tickers are still alive. They may have been bought out a good price eventually, but who knows, yfinance won't give you that data.
If anyone _does_ have 25 years of Nasdaq 100 open and close data they'd like to share, well, that'd be nice!