If you are unable to find the footage that you are looking for in the list of videos that the camera has recorded, there is a high possibility that your camera may have overwritten the file(s) that you are looking for. Once your camera's SD card reaches full capacity, the camera will begin to overwrite the oldest video files with new files as these are produced to ensure that it can save all new recordings that are produced. Once a video file has been overwritten, it is not possible to retrieve the overwritten file.
Most cameras also have a feature called 'Protect Event File' (formally known as 'Lock Event File' for older models) which is a firmware setting on the camera that enables the camera to store and overwrite impact 'Event' and 'Manual' video files differently to 'Normal' or 'Parking' video files.
This feature enables the camera to store up to 50 impact 'Event' and 'Manual' video files, before these are overwritten with any new impact 'Event' or 'Manual' files that are recorded by the camera. Generally, this means that the camera is able to store these video files for longer, allowing the user more time to access potentially important files before they are eventually overwritten. It is still important to access and download important footage as soon as possible as all footage will be overwritten at some stage.