That happened to me once in another company. The stock was no longer trading, but it continued to show up in my account, as a number. I never thought it still existed, though I did hope it would resolve itself. It didn't, and I had to sign some paperwork to get it removed from my account. Most brokers will explain that to account holders. I did wait a few years to do that, though. However, it shouldn't happen too much, unless you trade Q stocks, then I can see problems in timing the trades, and getting stuck with the result.
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