Well WC844 isn't EXACTLY the same as H335. It uses the same starting data but you really need to work up each lot of powder. I've used two different lots over the past 5 years, and there IS a difference in the equivalent loads for each lot.
The problem with pulldown powders, or any surplus powder, is that it is bulk grade powder and different lots will have slightly different characteristics. I have two different lots of WC852, and I can assure you if you use the same charge of the fast lot as you used from the slow lot, you WILL be wearing your rifle on your face.
Always work up each lot of powder, and don't try to shortcut it and use data from one lot for another lot.
I have two 8-lb jugs of WC680 that were given to me. I've never used that powder before. Considering the potential differences between lots, would you suggest that I go ahead and mix both jugs together thoroughly? That way, I'd at least have 16 pounds of an identical mixture and wouldn't have to re-develop the load halfway through.