A very simple answer is "until the next time the car crashes", you just replace the previous crash data with the new data. If the car requires that a certain a

A very simple answer is "until the next time the car crashes", you just replace the previous crash data with the new data. If the car requires that a certain amount of storage is always available to write crash data to, then it doesn't matter what's in that particular area of storage. That reserved storage is always going to be unavailable for other general use.