Corvette has has SIRs since 1990 and the SIR has always had some form of recording. As to what specific data is (or has been) recorded I'm not sure, nor do I know the length of the loop (it's probably a second or so), but I can surmise that over time, the amount of data has increased. I suspect in recent years, these recorders are saving throttle position, brake application, the VSS signal and maybe lateral acceleration. The loop is probably saved at SIR deployment.
My guess is, from a legal standpoint, post incident, the owner of the data is screwed because if he/she refuses to allow access, the insurance company and others investigating may take that as evidence of wrong doing and then they'll get the warrant. The question is, once some government entity, though a warrant, has the data, who besides them gets access after that.
Some have said, "Well, I'll just disconnect or otherwise disable the recorder". Bad idea. When there's an incident and those doing investigations find the recorder has been tampered with, then they have evidence of premeditation.
Any way you cut it, SIR recording is good for the car companies (they find out what happens to their cars in a wreck), good for insurance companies (they can cut pay outs), good for government (it can prosecute violators easier) but bad for privacy.