Yeah I talked to a lot of members of the prop department on Rogue One in researching a project of my own and what they told me was that immediately after production they scan almost all of their props for a digital archive. That way if it comes up some years later that "oh suddenly this background prop is important now" they have the model even if they don't still have the prop. I'm confident that's what happened here, they wrapped on the Mando S2 finale and the saber was likely one of the "new" props that wasn't in their digital archive.