If you ascribe to Trek's age old policy of "what happens on screen, is canon", then like @RedDwarf said, the evolutionary history of the Constitution class is now something like this:
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It's getting silly, but for those of us who grew up with the Encyclopedia, or the many people who construct models and love the starship aspect of fandom, I guess it's not impossible they are the same design being refit several times, even if highly implausible by today's standard.
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For those here who don't know, there was already a difference between Pike's Enterprise and Kirk's, which we generally attribute to a refit. I guess maybe it underwent another one in between.
Thank you for the composition of styles. I’ve been waiting for somebody to manage one.

And, yup, I’m perfectly fine with that refit history. The ship is modular, so the entire saucer or engineering hull may have been swapped a few times. In STO, you can do that at every major shipyard. In the novels - ST: Department of Temporally Investigations: Book 2: Forgotten History - the 1701’s engine assembly are grafted into another ship during the refit of 2270-73. nacelles, pylons warp core and all.