Just bought a pound of saf yeast from KA after realizing it was about $3/lb cheaper than my co-op bulk ady. Then three things happened:
I read in Maggie Glezer that any dry yeast won't keep, once it's opened, for more then two or three months and that it doesn't freeze well;
Hamelman says modern dry yeast is more resistant to freeze-damage, freeze at will;
I recalled that since embarking on the misadventure of sourdough, I use less yeast than I used to, so I really do need to store it or expect to toss some, if Maggie is correct.