Without posting the dozen or so pics for illustration, I will just ask the question. What is the likeliness of a proof or mint set with multiple or the same errors in them? In this case, all but the SBA have been struck through a thread, wire, or the like and the nickel has it on both sides. This doesn't include the state quarters or presidents, just 1c - SBA$. Is there a premium on something like this or just a keeper for the thrill of the hunt?
Virtually zero likelihood. More likely is that fibers got inside somehow, and that's unlikely enough all by itself.
I'll admit that I haven't kept up on what coins are included in the proof sets for the last 10 years, but when did they reintroduce the Susie B. to these sets? Chris