The chipco inventory included racks and racks of some chips, uncancelled, some of which was live.
I didn't get that part but racks of AC chips were sold here and on chiptalk. Supposed to have been cancelled but I know 100% some were not.
No clue whether this was the source of any of the chips in question but just saying it can happen.

Answering your question, while it seems a lot and unlikely, an overrun of 750 chips on an order of 30,000 is not a lot with a 200-300% profit margin. When ordering custom chips for myself, they often included the overruns free of charge. Sometimes an extra 100 chips on an order of 200.