You may have seen my comment. I was quoting my neighbor's speculation, who was career QA/QC at Boeing. Since then, we have the whistleblower's account. TLDR:

You may have seen my comment. I was quoting my neighbor's speculation, who was career QA/QC at Boeing. Since then, we have the whistleblower's account. TLDR: A bureaucratic snafu where the record keeping didn't match the actual work. The repair of the plug's air seal was miscategorized ("reopen" vs "removal") in the system, so did not trigger the required post-repair inspection, which would have (most likely) spotted the missing nuts. My neighbor said he'll look into the whistleblower's account, though he admitted it was plausible. Also: IIRC, castle nuts, which use cotter pins, are used for the plug's bolts. Meaning no tightening or torquing. The pressure differential keeps the plugs sealed. The bolts just keep the plug in place. If I'm wrong on that, please correct me.