Thanks for the replies. I thought it would be in the contract, too, but I've combed that thing multiple times and it only says, "All sales will be subject to xx% commission." All the language sounds like things refer to an original piece, and then prints can be made available to the gallery to sell in addition, ie. prints made of an original painting. There is no mention of a time period for sales.
I know it is best to just ask the gallery, I just wanted to ask on here first to see if there's a usual.