Given the issues at Boeing currently, mostly relating to a lot of strife between workers and management, and also with a lot of issues, regarding QC from subcontractors amongst others, having been found in recent times, not unlikely that the door was installed, and the person responsible for checking was meant to come next shift to verify, but never actually did, probably either because they were sitting with 500 tasks to sign off on, and 8 hours to do them, or was off the next day, and the next shift put the interior panels over the loose bolts. Either way there are multiple issues related to new aircraft on delivery on occasion. not good for Boeing, though the other major competitors also has reported issues with poor quality work on sub assemblies supplied from other sites, often needing to be scrapped entirely, and redone again. there are a lot of fake parts, or parts of dubious parentage, that also are in the spares lines as well, which has led to a few flights needing to divert due to in flight failures.