That is great. I bet he remembers stuff about specific coins, might be a good thing to discuss with him! I would leave those signed, dated folders exactly as they are. No upgrading, no filling missing holes, nothing. Just a nice time capsule!
I got coin albums from my dad as a kid. Now that I've gotten back into coin collecting I've started filling holes in the albums. Feels good to finish something he started (Like the Ike album) and lets me remember times spent collecting together.
Sounds like your relationship with your dad is as strong as mine is with mine. I dont know what I would do without my Dad around and I hope he is around for a very very long time. I also hope my son and my realtionship is as strong. I have some huge shoes to fill but maybe one day I will.
You could go ahead and add coins to the folders. Sign it yourself under your dad's signature and it will be ready to pass on to your son someday. Could put a mark by the coins you add so there is a history of who contributed what.
That is also a very good idea. I guess I need to think about that and figure out which would be best. Thanks