Oof, I bet that was a LOT of work! But it's so cool your creating books for your cousins! That's such an awesome, and I mean inspiring awe, gift for them.
Do you save all your TIFFs/PSDs? I save most until after I've printed. (I save ones that have a LOT of journaling. I'm bad at catching my own mistakes!) Anyway, if I save them, I rename the ones I keep so they have the same name as my JPG file. Only the Web-sized version I post in galleries has the same product-based naming system as the "kit in progress" TIFFs. It didn't even occur to me to rename the files until I found a mistake to fix before printing. It didn't take long to search (LOs are arranged by Year folders; TIFFs have their own subfolder in each year)...but it was still much more annoying than just looking for the exact same file name because of course I didn't notice the problem until I was frantically uploading before a SF deadline. But my copy-- the jpg, full-size copy--is always named yyyy-mm-MonDD-People_Event. So Christmas morning might be "2020-12-Dec25-Cal_Gen_Christmas_stockings." IMO that's a long file name. I try to keep it short, esp. since I also tag each LO so I can search quickly for people/events/places/years/etc/I'm insane about tagging.