Re the Titan / Titan-A situation, there is this background art by Dave Blass (Picard's production designer) that goes some way to explaining what went on:
[
SOURCE]
The thought being that the Titan-A is largely a new hull, but some components may have been salvaged from Riker's Titan after it was withdrawn from service after irreparable damage. Perhaps the computer cores, warp core, various other smaller bits and pieces. It's a 'refit' in a sense but it is also a 'salvage'.
It does make some level of sense in-universe given Utopia Planitia yards were destroyed over Mars.