I agree - and a subpoena would likely be too broad to be enforceable.
Why would a subpoena be too broad? Op has dealer name, description of the vehicle, and maybe even the date the paper plate was issued. Even without the exact date he would be able to limit it to the life of a paper plate prior to the date of the accident (90 days?).
How many cars of that make model and color do you think the dealer sold in the previous 90 days?
The one thing that’s odd to me is:
From what I’ve read the dealer is not required to issue a paper plate until 2019. Until then I understand the driver keeps proof of purchase handy to show the cop of stopped. Are dealers in California being proactive and issuing paper plates already
And some dealers list the vin # in their advertisements when advertising a car.