"And there is the TOS Enterprise's upgrade from her TOS-look to the TMP-look. She kept her registry and name. Now going from NCC-1701 to NCC-1701-A might be explained as a change in classes as the 1701 was described as "Enterprise Class" in the simulator label in TWOK and in TUC could have been a "Constitution Class". Note: I consider TOS as it's own separate continuity and the TOS Movies as "bridge" continuity that could work in TOS or TNG.
Thanks for reminding. Then Kirk's first Enterprise
was the first in the series if it's Enterprise Class.
The NCC-1701-A already is a different Enterprise
as it has transwarp drive (according to the bridge screens). Obviously a Constitution Class (according to Scotty's blueprint in ST VI) "II". I also favor separate continuities. Nice to see I'm not the only one.
"In anycase, the NCC-1017 Constellation could have been an older class but still of a starship configuration. Whether she was an upgrade that kept her registry or a replacement ship or the original we don't have enough information to determine either way, IMHO."
Yes. Though that shouldn't stop us wondering which explanation seems to be the most credible (unless we just go along with the VFX production reasoning...).