Lightroom Collections Disappeared

I don't use Lightroom a whole lot, but I noticed recently that collections I had from projects ranging from 1 year ago and later have disappeared in the last few months from Lightroom. By disappeared, I mean I cannot find any evidence that they ever existed in Lightroom itself. I've searched old backup catalogs and the further back in time I go, the emptier and emptier Lightroom gets to the point where any backup catalog from more than a year ago is empty. This is not a question of "I can't find the photos themselves" - as I'm aware they live on the hard drives I put them. In short, I can't find any of the collections in Lightroom (Classic), as those are effectively the project files. As some of these projects are no longer dormant, this is extremely distressing. Additionally, when solving this problem, I would (ideally) not want to remove any of the current collections I've created recently. Has anyone experienced something similar and/or know how to recover old collections like this?