“As I understand and would expect, construction techniques did not change only the formal registration process was done.”
I would agree with that.
“If these boilers were A.S.M.E. registered, it may benefit the new Form 4 work. “
I doubt that it would make any difference since the thrust of the Form 4 calculations is to determine the boiler’s condition today, not when built. Especially if the actual design was unchanged, ASME vs non-ASME, i.e no difference in strength one to the other.