Yes, I found a post on the NCRS site from John that said the 1968 model year was the first year for the "key envelope", so that's now been verified. However, before that I THINK they used the "Key Keeper" envelope (see below) but I'm not sure if it was a "factory" or a "dealer" item. It would be nice for anyone with older Chevrolet cars and trucks with original keys and glove box contents to chime in.
Ed