There are at least 87 threads on this topic, just from using one search term. BA's memory may not be good, but thankfully we have spreadsheets/notebooks/post-it notes decked around the screen etc. One option is to search your email for a term such as "Ticket Type: e-ticket" in quotes, since that for me always brings up reservations. It's less helpful if it's a call centre booking which doesn't get immediately ticketed.