My personal theory is that every version of a leve (both level and name) stacks up when we get a leve refresh, probably at random. So basically, you get your +4 leve allotment, but behind the curtain, you get, say 2 level 50 "Planks Aplenty" (sorry I've been leveling CRP most recently and I can't remember any of the ARM ones off the top of my head) and 2 level 45 "xxxx" leves.

In that way, if you do the 2 level 50 leves all you are left with is the level 45s. It's just my personal theory, but it seems to have panned out that way for me every time.