The registry number doesn't have to mean anything. During my favorite TOS episode, "The Doomsday Machine," they encountered a wrecked sister ship, the Constellation, NCC-1017. (The out-of-universe explanation for this is that TPTB bought an AMT model kit of the Enterprise to beat up and film as the Constellation, so the registry number had to be an anagram of NCC-1701.) That's "earlier" than NCC-1031. Also, in an era when they were making starships with five-digit registry numbers like Voyager's NCC-74656, they were still building NCC-1701-Xs. Finally, the Starfleet science vessel (the Grissom) in ST: III was NCC-638, as were several other members of its class later shown in TNG, etc (including the DS9 pilot). So the available evidence conflicts and may mean that the registry number refers to the class of the vessel instead of its time/date of construction.
There are also fan theories speculating on a possible Section 31 tie-in, noting that Bryan Fuller likes Halloween references, guessing at the possibility of a time ship or a ship lost in time but found in another era, etc.
There's also the significant possibility that the registry number will change from the trailer.
In short, I wouldn't attach too much significance to the number as indicative of the era just yet.