A few years back I bought a very messy collection online that was delivered in an old rusty lunch box. It had a number of good decent items in it, and also came with a big bundle of stamps on paper as advertised. When it showed up, it also had a couple of unadvertised surprises in it including an envelope stuffed with ~1300 4c Martha Washington stamps. They were a mix of 556, 585, 601, and 636's. I finally finished up processing the entire collection recently, and found two items in the large number of Martha Washington stamps that I thought some might find interesting.
First here is one stamp that had in inking problem down by the lower right numeral:

I thought it was interesting how the outlines of the numeral seems to be fine, but just some "filling" around it is missing the ink.
Second, here is a strip of 3 where you can clearly see the 3rd perf from the bottom is mis-aligned:

And here is the same strip from the back (flipped side to side):

I found this interesting because of some of the conversations in other threads discussing re-perfs. I thought I read that one of the things to look for is mis-aligned perfs. I can't imagine someone re-perf'd this, so I guess it is possible that perf "machines" sometimes screw up???