My understanding is that:
* DTT SD recordings are stored as unencrypted video streams - the file could be copied and opened by any media player.
* DTT HD recordings are protected by a key local to the box, which changes after reset. This is to prevent them being copied.
* IP recordings are protected by a subscription key - as long as you still have a subscription to that content, it can continue to be played.
It's all moot anyway. Some recordings will work in some scenarios, but nothing is guaranteed and it's not a supported scenario. Best to just reset fully.