Just took a look in the 1959 NEC Handbook (yep, I've got one laying around.)
It was added in 1959. Also, just as an FYI, the 1959 was the first year the NEC used the current numbering scheme.
Here is the text from Article 334 Armored Cable (yep, 334 was AC not NM back then):
334-2(a) Armor. All types of armored cables except Types ACL and ACV, in all sizes, shall have an internal bonding strip of either copper or aluminum in intimate contact with the armor for its entire length.