Boeing quality control could be hit and miss or its design engineering is lacking
Further investigation points to that Spirit the maker of the 737 airframes do ship it with this blank in place but only temporarily fastened. Boeing then take the blank out to load the interior and then reinstall it. The blank is like a door with a larger window and no manual opening mechnism and is being held in place by a frame rail with lugs but instead of movable pins and a handle like a normal door it is held in place with bolts and castelated nuts that should have split pins in them. As long as they are in place the doorblank can not be moved upwards (some say downwards and some later pictures of a locking bolt seems to support this) to a position where it can be opened / taken out. Again, regular inspection of these bolts have been made inpossible by having a complete panel on the inside. Questions remains over if split pins where installed. Bolted on parts can have the nuts unwinding themselves due to vibration. And the exact torque required to prevent this can be difficul...