I know a fellow brewer who routinely uses dry yeast ~2 yrs past its printed expiration date. He reports no problems with it. I have not used dry brewing yeast this old but I have used bakers yeast that was 6 yrs past its printed expiration date, and it made perfectly good bread. Yeah I know, totally different strains, not an apples-to-apples comparison, but the point is that dry yeast is hardy as hell. Two years old should be fine.