The very least pre 1990 or so. As the leading dealer at the time in Police/Safety cards ensured that Dr. Beckett got all those sets so they could be properly catalogued. The trade was he got comp ads in the annual guides.
He passed quite a few years ago so I can't ask him about any of this but I'm very comfortable. I'm not there to update the blurbs in Beckett but here are the cards which have been sold from 1971 on COMC. And in case anyone has a question, there is no confidentiality issues as I did this search from the web site
https://www.comc.com/Cards,ss,=1971+...ase~5d,ot,i100
Note it does appear the Nelson in Pink was actually a 1970 card. I can fix that based on the sheets. If you see anything else to be changed I can still change those after the fact so to speak.