What does Polygon do with delisted tickers?

Survivorship bias or survivor bias is the tendency to view the performance of existing stocks or funds in the market as a representative comprehensive sample without regarding those that have gone bust. We do not remove companies that have been delisted from the exchanges. We store the market data exactly as it happened on that date in time.
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We are also working on a ticker history endpoint that will show the full history of a ticker symbol including who held the symbol at what point in time and any changes that happened. This will include things like mergers, acquisitions, delistings, ticker changes, etc…