I am just dying to know how a CVR recording from a modern plane that has just landed get over written.
On A330s the CVR will stop automatically 5 minutes after engine shut down.
The CVR contents can be erased (by pressing and holding the erase button), or it can be overwritten.
In this case it seems that the CVR was overwritten. Usually that means that the aircraft was allowed to be flown on the next flight segment without first preserving the CVR recording.
Sometimes CVRs get overwritten when the electrical system gets re-energized for some other reason (e.g., ground maintenance test), although there is a protection system that's supposed to shut down the CVR again within a few minutes if the engines are not operating.
In most jurisdictions, when there is a "reportable incident" then
both the crew
and the airline are responsible for preserving CVR and FDR data, usually in coordination with the jurisdiction's safety board.
The correct procedure to preserve the CVR is to pull the circuit breaker, until all data can be downloaded and secured.