I use Satin Ice all the time, only use Wilton for dummy cakes (it's cheaper)I just made a cake and used Satin Ice Fondant, Vanilla Buttercrem, now that is delish!! Even better than the regular Satin Ice.
I think you are fine if they are in the refridge and not opened. I used them all the time in the same manner, no problems. As a matter of fact, where I buy them they keep them on a shelf not in the fridge.I guess when you think about it, don't we keep our jams and jelly the same way, and for the same length of time.