To me, it's an Occam's Razor thing. There was a ship called Enterprise, then it's blown up. So its crew are assigned a new ship. Also called Enterprise. Its a new Enterprise. If it was simply a refit, why wouldn't they call it by its old name?
Most likely because the ship had a new name. Whatever she was before, she was the Enterprise
now. Crewmembers who served on the ship under her previous name would really be the ones who would refer to that. Scotty would know her original specs, but even he would likely just refer to her as "the new Enterprise
." Ships being renamed isn't totally unheard of in real life. The very first U.S.S. Enterprise
(18th-Century) was a renamed ship.
They didn't change the name of the previous Enterprise in TMP, despite its extensive refit.
They were keeping the name, so they weren't changing it.
I mean, okay, there's nothing onscreen to say one way or the other but the other explanations seem awfully convoluted to me. And TFF certainly seems to support the idea that it's a new ship, with all the associated teething problems.
The same was true of the old Enterprise
after her refit. She had teething problems too--the transporter was unsafe to use and the warp drive created a wormhole moments after it was engaged.