Years ago BA used to operate a twin engine maintenance policy which dictated that similar maintenance actions would not be carried out on both engines (of a twin) by the same persons, unless a flight/engine run was carried out between one and the other. I think this policy was superceded by ETOPS.
If this incident, and it still is a big if, was the result of cowlings not latched, some serious quality control effort has gone badly wrong. The holes in the swiss cheese very nearly all lined up. The question is why and I will just say, there for the grace of....etc.
Replacing the oil caps after a Daily is critical & requires a duplicate inspection too...
Nightstop, are you sure about that?