> Given their nature the original intent was probably that they were secured at the factory and never touched
Specifically in this case, that factory being Spirit Aerosystems in Wichita where the 737 fuselage is manufactured. Part of the problem here is that Boeing in Renton didn't have processes for removing the MED when necessary on the final assembly line (in this case to rework rivets near the door). Without processes, there was one senior guy on the door team who taught himself how to do it, this was only needed a few times a year, but he was on vacation when this airframe needed the MED removed. Someone else did it (the NTSB couldn't determine who), the work wasn't tracked, and a separate team (the team literally sealing it up so it could be moved outside) put the MED back in but didn't install the bolts (which were gone).
Specifically in this case, that factory being Spirit Aerosystems in Wichita where the 737 fuselage is manufactured. Part of the problem here is that Boeing in Renton didn't have processes for removing the MED when necessary on the final assembly line (in this case to rework rivets near the door). Without processes, there was one senior guy on the door team who taught himself how to do it, this was only needed a few times a year, but he was on vacation when this airframe needed the MED removed. Someone else did it (the NTSB couldn't determine who), the work wasn't tracked, and a separate team (the team literally sealing it up so it could be moved outside) put the MED back in but didn't install the bolts (which were gone).