I've never believed for a minute that the Enterprise-A and the Yorktown were the same vessel. Star Trek V gives every indication that the Ent-A is a brand-new ship.
implicit in the ending of TVH as well IMO: "Let's see what she's got!"
The only reason why this debate even exists is because of the Ent-A's decommissioning at the end of Star Trek VI, and why Starfleet would decommission a seemingly brand-new ship after only a few years of service. But there are in fact several reasons:
5. Constitutions, a dated design in the process of being replaced, are retired instead of repaired if they are severely damaged. Remember that Spock intended that Valeris replace him:
"This will be my final voyage on board this vessel as a member of her crew. Nature abhors a vacuum. I intend you to replace me."
So it makes sense that the ship was intended to continue beyond the current mission, otherwise Spock's statement is a meaningless gesture. So what changed? Battle damage.