Why would you be more likely to notice after 11 months than 1 month? That fact is it is very easy not to notice if you’ve not been charged. The onus should be on the airline, which has already sent out a booking confirmation suggesting everything is ok, to contact the customer to tell them it is not.

This is a common IB problem - there are many threads about it and I certainly don’t think OP is to blame. Obviously he now knows of the need to check for an e-ticket number for future bookings, but the ordinary non-FTer does not know that.