Was OP's incident exclusively on BA or were there other carriers involved.
This issue is much broader than BA because IATA convention gives other carriers 72 hours to confirm space. While the reasons for this are an anachronism, the convention remains. If, after 72 hours, the other carrier does not confirm, BA should cancel and notify its pax.
All of this places the burden on the passenger to affirmatively check that there is an actual e-ticket # for every segment on every carrier of a route. This, in addition to a reservation.