That got to be so burdensome for the (now redesignated) BATFE that they decided to issue a blanket definition of 50 years old to cover almost all the items collectors covet. The exception, on request, of a specific gun or specific guns by serial number or characterization still exists.
You sure about that? I thought the 50 year thing was part of the original GCA 68.
It is certainly codified in 27 C.F.R. § 478.11, which is not something ATF could do without Congress.