Intriguing. A 31/32 century 4-digit registry on a starship without a letter suffix. I got nothin'!
Maybe Starfleet was being desperate and with inspiration taken from upgrading the USS Discovery, they decided to upgrade a really old ship in a similar way instead of building a brand new one (even though they have replicators and programmable matter that should technically be able to simply create a ship of a given size very quickly - we're talking inside a day most likely).
As for the ship not having a letter suffix... while it was never really confirmed on screen, people (in real life) suggested that Disco got a letter suffix because of the temporal accords... so most people (in universe) would see it as a brand new ship, as opposed to an old one that came from the past.
With this vessel not travelling to the future... its effectively an old ship that was revived/upgraded with modern technology... so a letter suffix was not technically needed.
Even the 1701 refit wasn't given an A suffix, remember? It was only given a suffix once the original was destroyed and a new one comissioned in its place.
Most of the time we see SF assigning a suffix letter if a ship is destroyed... but then in ST: Picard, we see the refit of the USS Stargazer didn't have the same number as the old one, nor a letter suffix (for that matter, the Excelsior refit didn't have one either).
Edit:
ST: Picard is a bit all over the place with starship insignia and starship classifications which didn't make much sense to me since neither ship was destroyed (at least not that we know of).
But its possible that part of the reason why neither ship retained their predecessor markings with a letter sufix was because they might not have 'distinguished' themselves like other ships in the fleet (such as the, Enterprise, Voyager or the Tikhov) and were completely different classess of ships as well - and for some reason SF just decided to give them same names without letter suffixes.
The Excelsior II is sticking out like a sore thumb in regards to NCC numbers though which is in the 40 000... or about HALF of what's displayed on the Stargazer (in the 80 000).
If we assume SF/UFP was building 1000 ships per year after certain point (because of technological advances and expansion), that would mean the Excelsior II was built around 2341 (roughly 30 years before Voyager)... this in itself doesn't make sense.
The only thing that comes to mind is that Excelsior Type II was made in 2341 (a 24th century remake) and given a 25th century makeover for ST: Picard S2... then SF made a decision to simply give the ship same name as the original (Excelsior) because it was the first ship of its class (or Class II Excelsior) and voila.
But then, why bother with upgrading USS Lakota in DS9 to rival the Defiant?
Why make the Obena class in 2380-ies which had pretty much looked like a 24th century version of an Excelsior clas upgrade (just with more oval saucer and sovereign style nacelles/deflector)?.
But again, to me, it would just make more sense if the Excelsior II and Stargazer as seen in ST:Picard were original Excelsior and Stargazer class ships from the 23rd century which were given 24th/25th century upgrades (effectively retaining the same class of ships as before just following a natural upgrade path)... and to that effect, they should have retained their original NCC numbers as well (but without the letter suffixes - or heck, give them the suffixes since the design of new ships alters their size, so it stands to reason the originals were harvested for the raw material and brand new/modern ones of the same/upgraded class for contemporary times were built).
