Originally Posted by
SamOF
Yep—AA's res system won't create a second PNR at all if it conflicts with one already booked.
Catching duplicates doesn't and shouldn't have anything to do with ticket issuance–it's about holding the space, not about tickets you may or may not have for reserved space. Think about a situation where a corporate travel agent is allowed to hold space indefinitely without ticketing; you still wouldn't be allowed to hold conflicting reservations.
Have had PNR on conflicting AA flights before. It does get caught eventually. However it certainly doesn't prevent a second PNR.