Question 1: Are you extracting thc beforehand or throwin the bud into the mix? I dont think this would effect the thc depleting more than it would effect the brownies going bad.

Question 2: Do you have access to a freezer?
becuase if you do than the shelf life is pretty much forever. Whenever I get a new batch of cookies i simply just put them in a tupaware container and have kept them for a month or two until they get eaten or sold. I think as long as the brownie itself doesnt go bad your in the clear.

however if you were to just throw your brownies in the freezer i would have no worries whatsoever, and they will keep for years as bud does.