"There is no canon evidence that the Republic was an older ship. Just because her registry started with 13 means nothing. The Encyclopedia lists it as Constitution class, so until canon evidence surfaces that it is not, that's what it officially is. And comics aren't canon."
I see, so the Encyclopedia is canon (how many solar years were "Space Seed" and Star Trek II apart?), but the comics aren't and neither is a design by Rick Sternbach. Interesting.
"Maybe that's because there was no "A" after the registry number?"
Just because they do it in the late 23rd Century doesn't automatically imply that's the way they did it in the early or mid 23rd Century. Just because they use four-digit-registries in the 23rd Century doesn't imply they couldn't use five-digit-registries in the 24th.
The whole "A" business originated with that Enterprise
design sketch from Matt Jefferies where he added next to "17th Cruiser Design" "1st Moderize & Modification 1701A
". So by the time of TOS (what we are talking about) the concept of adding an "A" was reserved only for modernized or modified vessels, not for vessels honoring the name of a previous one.
couldn't be NCC-1017-A. Looks like Starfleet wouldn't use this scheme until the replacement of the Enterprise
(compare USS Eagle
NCC-958(-A) which appears to be a refit Constitution Class Starship)
"FWIW, that registry was a mistake. The ship's registry was fixed as 71807."
I'm aware it was fixed, nevertheless the original registry hinted the existence of a previous and much older USS Yamato
NCC-1305 which I considered to be a nice addition to the universe of Star Trek.