That’s why I said “at least” since 1970.
My sources did not tell me since when. I had the impression, that it had been for years already in 1970. But I was not told that.
Mine are based on WTF moments during my travels and observations passed on by my Dad that grew legs after seeing dots and things around here.
That "since when" could very well include dates in the 30's if that tinfoil ain't adjusted just right....