They also have a different top fitting that the standard do-it-yourself ( DIY) adaptor hose will not fit.
At that point, you have two choices.
1. There is a style of filler adaptor used by folks who do it for a living that punches into the side of the can, thus bypassing the top connector entirely.
2. Fabricate your own adaptor. The fitting is a threaded nipple. Get one nut which fits that nipple, and another which fits the threads on the DIY adaptor. Epoxy/solder/weld the two nuts together, and you've got a fitting to attach old-style filler hose to new-style R12 can.
Voila! Air Fria.
Supposedly, you have to be a licensed technician nowadays to even handle R12 in the states. I'm not too technically skilled under the hood so I'd probably need help.