Charles Ellson wrote:
Aren't US banknotes also all the same size thus making it easier to
accidentally sandwich a high value note in amongst low value notes ?

They're all the same size, yes. Folks do occasionally make mistakes,
but that's not a major concern (other than for the blind) in bill design
compared to anti-counterfeiting features.

One of the old tricks was to take a $1 bill, bleach the ink off, and
print a $100 bill's faces on it. This got around the checks specific to
the material used, since all bills until recently had identical cloth.
Newer bills have security features that prevent that -- if cashiers
bother looking for them.

S