That's it, though, they aren't starting over again, and there really was no indication that no new ships were built for a century (indeed, we saw lots of new designs in service, and some may have been post-Burn). The Burn made warp drive more difficult and severely weakened Starfleet, but the institution continued onwards regardless. So having ships with higher registries isn't awkward or unnecessary, it's just in keeping that Starfleet didn't truly stop after the Burn. It think hull numbers in general should be regarded as window dressing and nothing more, IMO...