So one thing one considers a lot, is taking each bin separately, and combining them.  I don"t know how hatd either of those are, to do.l, but to

To consider whether that is reasonable to do or not, we imagine trying it.

If I have one bin from a histogram, and I consider this histogram was sampled from a population described by another, there might be only so many ways of sampling the other histogram, to fill the one.