I'm generally content to ignore the whole Enterprise/Constitution II
class question, but here's an idle thought: What if the difference between Enterprise
class (1701 refit) and latter-day Constitution
class (1701-A) comes down to interior configuration rather than exterior? The refit and 1701-A have the same hull design, but notable internal differences. Notably, while the refit's shuttle bay is the rear part of a vast, open cargo complex filling much of the engineering hull, 1701-A's shuttle bay is in almost exactly the same configuration as the TOS shuttlebay and doesn't connect to a forward cargo space. There are also notable differences in the configuration of the bridge, engineering, sickbay, the officer's lounge, etc.
And there is an external difference as well, in that 1701-A doesn't have the pearlescent hull coating of the refit 1701. Apparently there are some other minor physical differences to the vents at the rear of the dorsal and the three "space-energy field attraction sensors" around the deflector dish, plus a change in the window configuration of the secondary hull, according to this thread
So could that explain the discrepancy? They're different classes because they have major internal differences and slight external ones? (Although I gather those physical changes to the sensors and vents happened around TWOK or so.)