https://www.reddit.com/media?url=https%3A%2F%2Fi.redd.it%2Fm...
there are three visible on the right in that photo. These bolts don't have a cotter pin and they look like they are essentially part of the plug door assembly itself. It sounds like they are never intended to be loosened for installation, opening, inspection, or access. They bolt the collar that goes around the guide cylinder to the plug door frame itself.
I think if these bolts become loose, then 1) the collar will be free to move upwards, assisted by the spring that you can see in that photo below the collar, and 2) the door plug is basically mechanically untethered and just held in place by friction and air pressure. If the plug door frame itself were nudged up about an inch by the collar spring action, or any other force (like turbulence), it'd push right out like DB Cooper.
In the NTSB briefing, the chair said that the NTSB had offered party status to Spirit Aerospace (who I think make the frame and the plug) and the machinist union.