Can't tell you the FIRST year for GM.
68 Chevelle wagons used it. I put one on my 68 El Camino to hide the receiver hitch. Looking at pics of a 65 & 67, apparently the filler is on the side. So, maybe 68 was the first year for Chevelle. Not sure about previous years.
According to this article, Ford first did it in 1952.
https://krcgtv.com/features/beyond-t...as-filler-caps