Auto A/C R-12 vs 134a Q

Back in the R-12 days IIRC a car took (3) 12oz cans or so to fill totally from empty, now I just noticed with 134a that it takes about 1 can, 11-16 oz is on the label under the hood. Has there been any advances in the amount of refrigerant used, or is that less is needed for 134a or something else?

Several factors are involved. Larger cars have bigger systems than smaller cars. For a system of a given size, its R-134a capacity is about 80-90% of its R-12 capacity. There have been advances in efficiency leading to less refrigerant needed. Chances are what you’ve observed is due to a combination of these things.