I hadn't made any adjustment to the save settings, or anything out of the usual whatsoever.
I'd been working with/saving the files dozens of times across several days and sessions, so they definitely were successfully saved initially, or I couldn't have been continuing each previous day's work, etc, over this period of time. These were sequences that had existed for several days but when I opened the project last night, they were just gone.
(Attached is a pic from my auto-saves folder - the files should be between the September 2 saves, and today's.)
Any thoughts on this would be greatly appreciated. (Let me know if any clarification is needed!) This is about 50 hours of work that I happened to be really excited about too, and fear I won't be able to replicate, hahaha. I could cry y'all.