Why don't we see 6ds significantly defaced with crosses from the same period, except on the rare occasion where perhaps it's used to defraud a 6d? Otherwise it's an exclusive phenomenon to the Shilling! X/XII scratched on shillings, which doesn't draw me to defacement...instead, at best, a ritual from J6 that had to deal with unmarked Elizabeth shillings, which then culturally continued thereafter, as best I've understood it to date!
X or X|| scratched on an unmarked or worn Shilling (in the masses and consistencies with which it happens), with all the other variants (fraud, mistake) inbetween, is a no-brainer for me.
I'm sticking with the sensible tudor, and subsequent Stuart community solution to big coins, which had to deal with clipped coins, and the introduction to the peasant communities of a new denomination...makes social and numismatic sense to me!