I think a big factor on this subject is how hot you run your loads. If one lot produces more pressure than another, a given load might work with lot A but be too hot with lot B. If you mix them and do load development, the danger is you don't really know what percentage A vs B each case has in it. So a bunch of rounds might be safe, but if you get one that for some reason has a much different mix, it then might be over pressure.
If you run loads well below max, then it might not matter. But I did I have this happen to me. I had a load I was working on, and had tested previously with some H4350. I was just below max. Later I had two jugs with a small amount in them, one old and one new. I mixed them and loaded up more of the same test load, and now the bolt was very sticky. Temp conditions were similiar.