Mycorrhizae in dept. store potting soil - useless?

I read somewhere that if mycorrhizae isn't stored at a certain optimal temperature, it dies or degrades.

If that is true, then those bags of potting soil with mycorrhizae left out overnight at department stores (where I live anyways) where temps can reach below freezing at night, and then during the day, can get to near plus 20 Celsius, should be avoided?

yes its true for most things, if theres storage instructions, you follow them