What was the method of receiving the subpoena btw?
Email. I suppose I could have demanded a hardcopy, fought about the jurisdiction, etc., but this wouldn't have done anyone any good.
You should have at least called in to the DA's office to check it was a valid subpoena, there could be liability if you release information to a spoofed subpoena. Someone (with motive/connection or not) could have sent you that email spoofed to the DA's office about the credible case, without it being from the DA.