I would think that velocity changes and pressure issues would be caused by powder sensitivity to temperature rather than lot differences.. I would just shift over to one of the powders that are not sensitive to differences in temperature, such as the Hodgdon line of extremes. Either that or just use the same loads as you did last hunting season, heck I've let shells sit for ten years or more and never had a single problem, they shot the same as they did..there's a lot of bull out there and sifting through it is an adventure..