Personally, I subscribe to the theory that it's a brand new ship. Nothing in the dialogue from Star Trek V supports that it was a different vessel renamed Enterprise.
That's my take on it as well. There was a new Connie being built, perhaps the plan was to name it the USS Ti-Ho or something else, but soon after Fleet Admiral Morrow decided to decommission the Enterprise (or maybe after its destruction at Genesis), the decision was made to name the ship in honor of NCC-1701. Kirk and crew had no knowledge of this and were suprised to see 1701-A because they'd been exiled to Vulcan for three months, during which the change in name had occured.
"Canon is only important to certain people because they have to cling to their knowledge of the minutiae. Open your mind! Be a Star Trek fan and open your mind and say, 'Where does Star Trek want to take me now'." - Leonard Nimoy