James890:
Data remanence on CVR?
If they were still using magnetic tape, then there may be a chance to recover earlier recordings, much as overwritten hard drive data can sometimes be recovered if you have a right tools.
However, I would expect that modern cvr systems would record to flash or battery backed up memory. ie: digital rather than analog recording. Earlier contents would be overwritten in a continuous loop from the start of memory once end of memory is reached. There would be no way to recover data that has been overwritten...