It stores one start/finish per SD card. Make sure you mark it on the track not in the pit lane or grid. If you mark it again it overrides the current one. Easiest to keep separate SD cards per track imo or you can backup/restore the start/finish line file for each track on a single card. Also I use MicroSD in a full sized adapter so I can copy the video to my phone for review between sessions. If you get a card above 32gb you need to format into FAT32 on a computer beforehand. Make sure it is set to Track in the choose video overlay section before you start recording. Put some painter's tape over the mic cutout on the driver's side plastic A pillar near eye level to get rid of annoying wind noise that you get on the recording when driving with the windows down.
Also if you're not familiar with it, look into the performance traction management (PTM) modes available that you might want to try.
https://www.camaro6.com/forums/showthread.php?t=496996