My response was intended for Automotive use. While in some very, very, very, old home systems the R12 while the formula may in some circumstance be the same as offered for the auto industry there are not many that will or do use it for their classic vehicles. I do know that before auto dismantlers were required to drain AC system many capitalized on the R12 market when the manufacturing and supply was ending by pulling them from cars AC and selling it.. But as far as I remember not many used any refringent for their vehicle's except from another vehicle or marketed specifically for auto mobiles? In the last days of R12 buyers for automotive use would specifically ask about the manufacture and want to see the can.My understanding is that R12 is still available abeit expensive. HVAC techs recover it from older home A/C systems when they upgrade the customer to a new system.
I am not a historian of R12. I am sure all this can be found researching it on the internet? In my early days of Hot Rodding the AC systems came off most of my cars to lighten them down.
I really wont even work on old AC system using R12 anymore. It is a PIA to get parts. It's easier to do a conversion to R134.
I do still own a complete R12 tools gauges and even a few those old style "GRANADE" puncture can and handles of the day. Pleeeeeze don't make me post a picture of all the R12 sheeet I have makes me feel really fricken old .