It is also possible that the customer could order another for-end for said barrels if wanted at more of a price.
If a customer sent gun back for another set of barrels, they would be serial numbered to gun and most likely another for-end made with a number 2 stamp on it as well. The original for-end could be made to fit the second set of barrels but quite possible Hunter Arms did not want to tie up a worker to do such a job.
I have done this more than once and it takes longer to fit the for-end then it does to fit the bastard barrels on another gun. You cannot alter the loop on the original barrels to fit the other for-end it all has to be done on the new for-end metal.
That's my theory and I'm sticking to it.