You're probably right about the gelatin. I chucked away some Kwik-Clear that I'd had for a few months because the gelatin started to stink. Buying separately and using the powdered form could be a good plan.Sorry, I don't know. My guess would be it's down to the gelatin which is made from pigs trotters or cow hooves so I suppose it may go off after a while, but is apparently stable in powdered form.
At least I hope it is!