I've been between computers so I apologize for the delay in response as I pulled up the development copy of the game. I looked at the coding and it appears that I've recently set it to key off of the unreleased boss of the Khrono Tomb. I can look into uploading a bug fix build to restore the game overs appearing based on defeating the gold statue. In the meantime, if you lose against the desert bandits/lamia and witness the Game Over then run away/win the battle it should also unlock in the gallery for the current version.
Keep an eye out for the WIP Bug Fix Build in the future which should restore the easier method of seeing the Game Overs for now.