Woke up to a nice Christmas bonus this morning. I had sold calls on a French stock that expired yesterday deep, very deep in the money, but somehow were not exercised. No idea what happened on the other side of this position, as to my knowledge all brokers automatically exercise and you'd have to very explicitly override to have this happen to you. I've been selling options for quite a while now and can't remember that ever happening to me, only a couple of times when strike was very close to share price. Anyway, this got me thinking: obviously, open interest data is public, but for obvious reasons generally only list series with future expiration dates. Is there any source out there that shows the open interest after a series expires? In other words, somewhere where I can now see the open interest for the December 16 expiry? I would be curious to know how lucky I really was here in general or if money is being left on the table quite regularly. Thanks!
Wow, congrats to you then! Are you sure there's not some administrative delay with your broker and that an exercise message comes in on Monday?
There is by definition no open interest after expiry, as the option is already voided. So the answer to your question is clearly no (i.e. not available and applicable). BTW from a very limited sample size I know strange (non-)exercises do happen quite regularly. But in your scenario it is more unlikely, it surely could have happened but at this point you should still be prepared to get a (delayed) exercise message...
Thanks all. Some more searching and I can answer my own question: for US options the OCC has data on their website: https://www.theocc.com/market-data/market-data-reports/series-and-trading-data/series-search. At least yesterday and today they did, I'm guessing tomorrow the 16 Dec series will be gone. Went through the top 20 option stocks series in terms of volume: that's hundreds of series and (I'm guessing) millions of OI and found only one (!) contract that some poor soul forgot to exercise. SPY 16 DEC 300 (with SPY trading at 383) had an OI of 1 after expiration. Everything else deep in-the-money was zero on every single series on every single stock. It might be different on European stocks (I'll check if I can find data), but the chance of this happening to you in the US seems to equal winning the lotery.
I got a message from IB telling me the series had "expired" (which is the message you get when your option is not exercised, opposed to "assigned" when it is). I guess they could have misplaced the assignment notice, I'll see tomorrow.
I assumed with French stock you meant Euronext (Paris), not a French stock listed in the US. If so the exercise behavior might be different than what we are used to with the OCC...
Euronext published a daily statistics file today which included the 16 DEC series. All series, in- at- or out-of-the-money, had an OI of zero. Contrary to the OCC, they seem to use your definition, i.e. there can't be any open interest after expiry regardless of whether an option was assigned or expired (which makes sense of course). Didn't get a delayed assignment notice, no shares were taken as part of the assignment and the position has been removed from my account. So, yeah, it seems I won the lotery. Still not sure what the odds were on a Euro-stock though, altough it's hard to imagine this happening all the time.