It would be fun to learn that NCC-640 had been right all along, as that would remove some overlap with the good old Cygnus
class... But considering how Mike Okuda got his information, it does look like the model underwent some refitting between ST4 and TNG.
It's nice to have all this ambiguity in both the versions of the TNG episode, as I, too, would like to believe in NCC-640 in my personal delusionverse. OTOH, there are plenty of other Oberths
with five-digit registries (either exactly known or fuzzily glimpsed) to support the idea of ongoing 24th century construction of the type. Or perhaps major reworking, which involves decommissioning and recommissioning.