The rifle is in such good condition that there are no tell-tale scratches or wear marks that I can see to indicate that the disk has been swapped.

And with the greatest respect Woody 99, Dana Jones says (P.169)that "3" was possible (why else have a 3 available on the disk", but worse than 3 meant barrel replacement.
As I already wrote, this is an academic point. Important is how the rifle shoots now!