As I recently learnt, all U.S. stocks are part of either Tape A, Tape B or C. Stocks listed on the NYSE are on Tape A, NASDAQ-listed stocks are on Tape C and everything else is on Tape B.
Of course, if a stock is listed on some exchange, one can trade the stock there. However, many stocks are traded on multiple exchanges. In this case, how does one determine where the stock is listed? Is it based on the exchange where it first started trading? What if the stock is traded on multiple exchanges right after its IPO?