I've been in at least two apartments blocks that had multiple post codes, but that's not hugely unusual as a UK post code is (to a first approximation[0]) a street identifier, so the high street has one, the side street has another, and the rear parking might also be its own.

In one case, this meant my front door and back door had different post codes, even though it was a 35 square metre one bed apartment.

[0] except when it isn't https://en.wikipedia.org/wiki/Postcodes_in_the_United_Kingdo...