I love this kind of discussion, but would recommend not taking Starfleet registries too literally or treating them as fully sequential when attempting to dissect starship lineage or production order. There have been enough inconsistencies, both unintentional and intentional that I think we are left with no choice to assume that Starfleet registries are generally but not totally sequential. My general impression is that intentional loopholes were left for the writers in this area, knowing that future unintentional inconsistencies will arise.
Regarding the age of the Constitution class, I do think this is a very open topic. The famous "dozen like her" line from TOS leaves a lot of wiggle room. We don't know which, if any, of those dozen we ever saw in any production. Maybe all the ones that we saw were, for reasons not obvious to us, not amongst this fabled dozen. If you're going to treat NCC-1017 as an older ship that was refit, you're likely forced to do something similar with NCC-956. For that matter, what IS the Constitution class? Was the Constellation ever called this? For all we know there were a series of very similarly shaped starships launched in the early half of the 23rd century that were all "Starship class" but not Constitution class.
I think there are similar mental gymnastics that can be done to put, say, NX-1974 with refit design before NCC-1975 with TOS design. I mean, having NX/NCC-2000 be launched in 2285 is pretty weird too. They should have hit NCC-2000 around 2260-2265 if things were as linear as we might want them to be. Maybe prototypes get reserved early, as soon as a project is ordered, not when the ship is commissioned.