The BA 757s were a bit of a mess in terms of registration.
First reservations ( at £90 a pop ) were G-BIJG to JR. Cancelled and re-reserved as G-BIKF to KY and then each one of those in turn was cancelled and reallocated to different airframes in the batch. No idea what was going-on there!
e.g. G-BIKR was originally for cn 22187, but that airframe was moved to G-BIKO and 22189 took G-BIKR instead of being G-BIKT.
G-BIKZ was tacked-on a couple of months later.
So, to reiterate the OP's question... whodunnit? Who makes that decision?