Supposedly it has an ignition inhibitor to prevent ignition in a vehicle when the evaporator develops a leak. You are correct in stating it is NOT R12. Any shop doing AC repairs will be reluctant to work on it if they are not sure what is the refrigerant. They are likely going to put it in a scrap bottle for unknown disposal, and charge extra. Yes it is a cost to convert to R134a, but the R134a ports will be installed along with required seals and anything else required. A R134a label should cover the original R12 label so the refrigerant is known.