imo, you use what works in YOUR personal gun safely. max loads can vary widely among different sources of data. a load manual is a GUIDE that show what results they had when they tested/experimented with at that time, in that place, and in the equipment they used at the time whether it was an actual gun, or some other sort of pressure testing equipment.
each person is responsible for carefully working up his own load, under his conditions, in his equipment, and observing what is going on and knowing when enuff is enuff.
these are my thoughts on it anyway. max charges can vary several grains among different sources, and it is our duty to play it safe n work up from a lower charge to find true max in our gun.......n each gun can be different.
i reckon technically one should work up again with each new powder container, but that seems extreme unless there were radical powder changes, or you were nearly over max to begin with.