For xerographic (and other chemical process) prints, what you say is probably true. For relief printing (think Gutenberg), this convention seems reasonable, tho

For xerographic (and other chemical process) prints, what you say is probably true. For relief printing (think Gutenberg), this convention seems reasonable, though you'd have to grind, not scratch, away the extra number. I don't know enough book history to say whether this convention is old enough to have started from relief printing, but that's the only way it makes sense to me.