So how do you specifically differentiate between the formal offset printing technology and an accidental deposit of ink on the back of a stamp?
Why not just adopt offset and set-off?
Not understanding the question.
I will say that the term "set-off" is an awkward term that seems invented by some that think that others are too obtuse to understand the difference between a printing method and ink on the back of a stamp from contact with another wet stamp. Context is everything and if someone is asking about ink on the back of their stamp or someone else is told to look for ink on the back of a stamp to prove or disprove something it seems a folly to have to dumb things down by using a "special" word. Why can't "offset" have multiple meanings? Most audience members will get it.
Edit to add:
The PF uses "offset"