Do two part solutions expire?

I don't know if they do, but I had some that was really old (a couple years in my storage room). What I did notice is that one of the parts had crystallized out of solution a bit, probably from low temperature, and was all full of white crystals. The bottle mentioned warming it up to dissolve it if that happened, so I did and it was fine and I used it. Just set the bottle in a sink of warm water for a while, and after it warmed up shook it up until everything dissolved again. Used it slowly over the next couple months and didn't see any problems in my tank, but that was just once instance.