The distallates could come out of suspension, leaving the base products (which may include crystals and other harsh products) to dry and become ineffective. They may not re-mix even with vigorous shaking. I would not use it. Just my 2 cents.
I've had two 8 oz jars of Zymol Creme and Carbon paste wax in my refrigerator for about 4 years now. Yes, the instructions say to store in a refrigerator.
I wax often, every 2 - 4 months and you use so little it seems to last forever. It looks and smells like the day I bought it. I just got done waxing the 300C and the 300M today and they look great. 8)