This is the kind of thing I was thinking about
Yorktown bridge (unaltered):
The bridge module used in the next two movies is obviously different, but if we accept that Enterprise-A is a reconditioned Yorktown then the change of bridge modules makes some degree of sense, as Mister Scott and his team have been welding new components over the top of the old ones. The ship seen in TFF is a 'new' ship... from a certain point-of-view.
Wouldn't all Constitution starships have the same bridge design?
Well yes, that was the point. When we see the above bridge in Star Trek IV, the new Enterprise has just been given to Kirk so it's still using the original bridge module from the first three movies. Or, more to the point, it's using the USS Yorktown's
bridge module, as the only thing Starfleet has done to modified the ship is to change the decals on the outside. But when we see it in Star Trek V, the same Enterprise has got a brand new bridge design, indicating that a new bridge module has been airlifted in to replace the one used when it was still called Yorktown.
I think it indicates that 'in universe' the Enterprise does change between tbe two movies. Which might further indicate that, whether it was previously the Yorktown or not, the Enterprise that we see at the end of Star Trek IV is at the very least a Constitution Class (refit) ship that had already seen service. Not a brand new build straight out of spacedock. It was modified to a newer spec in the next movie.