I defrosted a litre of base I made over a year ago, it was delicious. I store my base mix in litre lots in self-seal heavy plastic bags from Sainsburys, carefully pressing out any air before I seal the bag.
Theoretically if you keep your base frozen it should be OK for many years as it cannot deteriorate.
Incidentally, as I love Thai food, I also store my fresh Makrut leaves in plastic bags in the freezer, and defrost only how many I use at a time, and I have yet to notice a loss of flavour or aroma when they're defrosted and torn across.