Henry
Autoexreginated
I may be crazy, but I'm pretty sure the 1990 BECMI Rules Cyclopedia has studded leather......I have it on my shelf, and I'm almost certain it did. I'm out of town at the moment, or else I'd go check.
Nope, it doesn't -- I've been prepping with it for a game for a gameday in a couple of weeks.
Earliest mention I ever saw was the 1E PHB from 1978, and the White box from 1974 doesn't mention it, but that's not to say a reference from one of the supplements (blackmoor, greyhawk, etc.) didn't have it.