It would have been around 1990 or so that it started changing. I think it was in the late 1980s that I had the account with the fax service, and it was a couple of years into it that I needed to send in the form stating my need for the information, in general terms. It stopped operating completely at some point after that.
Your reference to fax dated it to the 1980s. I made good money in that era servicing fax machines. Anyone could request practically anything and they would be given the information because they had a "secure fax" number.
To many nuts on the road now days know what those plates mean and its an its an easy effort to plug the call into Google and get your address if its not a PO box. I saw it happen many, many years ago. Took my plates off in the late 80's. Don't need the advertisement. Ken