Current refrigerants are also very good, they're just more expensive.
I doubt the refrigerator from 70 years ago had blown foam insulation (polyurethane insulation was introduced in refrigerators in the mid 80s), so it probably had terrible efficiency. It may have clawed some of that back by lacking automatic defrosting.
The process didn't change all that much, neither did engines used in compressor so it is mostly "how well isolated the fridge is"