It doesn't make a lot of sense IMO to take the saucer section of a Saladin-class ship and make a new Contitution-class vessel out of it. After all, despite outward similarities, the interior components and layout of a Saladin-class and a Constitution-class saucer have to be vastly different
My "in-universe" explaination was that they had numbered it the same as an earlier Constellation. However, it was a different numbreing system back then, and instead of adding a letter (such as ncc-1701-A), they just used the same number.
^ And this. The Constellation
's 1000-series number is unusual among other Constitution
-class ships, but that difference is nothing compared to, say, the Enterprise
-D's 1700-series number sticking out like a sore thumb among all the other Galaxy
-class ships in the 70,000+ range.
Also, it seems there is already a precedent for re-using a number without an "A," and in the form of the Enterprise
herself: we all dutifully refer to the TMP version as a "refit," but really it's a completely different hull. Every detail, from the top-level design lines to the room and corridor layouts down to the buttons on the consoles seems all built from scratch. After all, Ford doesn't take all of last year's Mustangs and bring them in for a "refit;" they design a brand-new car based on the previous model's ideas, with modifications. Chances are, everyone just thinks of it as "still the Enterprise
" for sentimental reasons, when common sense and our own eyeballs tell us it can't possibly be the same hull.
But if that idea is unpalatable, then we can still eat our cake and have it too, by imagining that the on-screen Constellation
is a "refit" from an earlier similar design that we never saw.
In any event, the Saladin
idea sounds fun at first listen, but just doesn't hold water, as others have already shown.