As long as it was kept in a dark place and away from heat they should be fine. I know people who just keep tabs in their wallet for years. 

As long as it was in the dark for the most part it should be good. Incandescent light can degrade it to some degree, but not like sunlight would. 

How much will this affect potency? They've been in a bag aswell so not much heat or light has got to them but I'm wondering as I have never wrapped them in tin foil

Kept some tabs in a baggie in a glass jar with no tinfoil wrapped around it