I hope this doesn't sound too geeky. (What can I say? I like cars...)
It's true that VIN numbers, as we know them today, did not exist at the time, but the 452 was not a regular production line vehicle.
These vehicles were hand made, (Often to the customer's order) and the bodies were therefore marked with either Style/Body or Model/Copy numbers, which do serve as unique identifiers today.
(The engines were also numbered, but that is a far less reliable identifier for obvious reasons.)
Rutherford had 452's at his disposal on both the East and West coast. The California model was a convertible coup and the New York model was a four-door convertible phaeton with the distinctive two-piece speedboat style windshield.
Given that both appear to be 1930 models and the sheer uniqueness of these vehicles, it would not be too hard to track down surviving examples, if any exist today. Tying one to Rutherford and the JW's would be a different story, as provenance can be pretty shaky.
Rutherford was apparently no stranger to the Cadillac. Here, for example, is picture of him with an earlier 1928 model similar to one that Al Capone owned. (Note the visor and reverse swing of the rear door)
If we were keeping count (LOL) this would be a third ultra high-end Cadillac that we can tie to the Judge.