Everyone can request discovery. But, requesting it from the DA does not always work because the DA is out of the loop in traffic matters in CA. Many will do as your DA's office did - they send a request to the agency involved to provide the defendant with discovery. Others just say they are not involved in the process. In those instances, you either have to seek compelled discovery from the court, or, you make the request from the law enforcement agency. Many agencies will comply with these requests without being compelled by the court. The CHP tends to be very cooperative.
But, you did not prevail because of some wise discovery practice, you prevailed because the state's only witness failed to show. You will never know if your strategy and trial prep would have prevailed or not. You will never know whether or not the officer's alleged failure to follow agency procedure in some way would have translated to some sort of legal insufficiency. In most cases, the court is not going to be concerned about a policy violation so much as they are about the legal requirements. But, not knowing what policy issue you intended to raise, it's hard to opine on that aspect of your potential defense.

