I bought I case full of 50 round boxes from Midway, so I've been reloading in lots of 50. The problem is when it come time to tumbling it's easiest to just dump 150-200 cases in the tumbler. So the 1x fired get mixed in with the 4x fired.
I sort mine by 100 round boxes. Your 50 round method is just as good. I have a question though, why ammo fired 1x and why some 4x. Different load? If so, I wouldn't mix the brass!
For most of my center fire revolvers I have two different loads. One load is mild and easy to shoot 100 rounds in a day. The other load is full house hunting or silhouette load for accuracy and usually is uncomfortable to just go out and practice with (and usually more expensive). The brass for these loads react differently due to the pressures. They do blow out a little differently, and can minutely lengthen. Then when you size them, you work them again. Pretty soon your brass is mixed. It is not the same. These suttle differences change your accuracy and you wonder what is wrong with your gun.
In my experience, the difference in accuracy and case life is good reason to keep the brass seperated. I have the recipe of the load in the top of the ammo box. When I finish filling the box after reloading, I change the number of times loaded + 1. Most of my mildly loaded brass will last for 3-4 more loadings than the hotter stuff. When the cases start to crack or shows signs of problems, I know they all will, and as previously posted, I toss the whole box to be safe.
It is easier to dump 150-200 rounds into the tumbler. I usually shoot a couple of different guns, so I can throw in 100 357s and 100 45s with no problem. Still keeps them seperated.
Good luck with your loading. You will get lots of advise here. Use what you can, file some, toss some.
Steve