I've a friend (professional landscape photographer in Colorado who started out as a physics PhD and systematically approaches these questions with precision/accuracy) whose word I trust completely. He reports that TMY and 400TMY (not necessarily TMY-2; insufficient long-term experience with that one yet) do not age well at all, even when kept in a freezer their entire storage lives.
Originally Posted by Ryuji
The same friend indicated that 100TMX and 320TXP sheets age very well under those same conditions. It was based on his input that I decided to stockpile a large quantity of 320TXP over the last year, mostly 5x7 plus a bit of 8x10.