And don't forget to look under the bed tonight.
Kids, don't try this at home.
Every since I've been reloading (yeah, yeah, backin my day.........yada yada) I have made a practice of when I get low in a can of powder, I open another and make sure it is the same sort and that it looks alike and then I add the one to the other. I then roll and tumble the can to mix them well and go on loading. I have never had a problem. Unless you are already running the ragged edge of disaster any slight variance in powder will be unnoticed. I've heard these stories about some fellow that opened a new can of powder, used an established load (of course, it was totally safe) and ended up with no fingers and smoking shards of steel in his head. And it's always, "I know a guy whose brother-in-law's cousin's uncle's buddy etc etc". I have also seen the notices of recalls where a totally incorrect powder has been put in the wrong packaging. But you notice, I not only look at what the packaging sez, I look at the powder. I don't think I'll be mixing any 4350 with H335 any time soon. This is not a dangerous hobby but you do need to have your brain in gear.
I think we are blest with the consistancy of our components.