Update:
So I was previously only looking at the main page for my reservations, but I found there is now a "my trips" function on the iPhone app which lists out all reservations, including recent past trips... It appears this is a way around trips "falling off" the main page... you can simply go back and look them up here (e.g. if you are using a keystone unreserved that was purchased for a previous day that is no longer showing on your home screen).

Juggler - I can't wait to hear your experience using out of sequence keystones reservations.