TL;DR; Available duplicants change every time the game is loaded.
I'm in Cycle 25 right now and kept the latest available duplicants to choose on of them later when I got things ready for him. I saved the game and loaded it later on and the original choice of duplicants was gone and three new were available. This seems to happen on every load. I attached the save file in case it does not happen generally.
1. Save a game with new duplicants available 2. Take a look at the duplicants available 3. Load the save 4. Look at the duplicants available again