That is amazing.
I re-sized the pics to put them side by side for
comparison of markings. Size differences can not
be judged though. The resizing didn't come out
perfect.
I marked all the identical stains, folds, and
accidental pen marks in
red.
I then marked all differences making each cover
unique in
green.
Edit:The top cover has a yellow hue in the scan/pic. It is unnatural
as it extends clean into the color of the stamp. I ran it through
photo shop, using the stamp ONLY as a baseline, as that is the
only thing between the two that wouldn't have a variable... I
equalized the hue using the 'clean' stamp. When the top stamp
equalized to the hue of the bottom stamp, the envelopes were the
same color.