All indications here (from the NTSB prelim and the widely reported whistleblower account) are that during rework for a minor manufacturing discrepancy, the mechanics on the shop floor followed bad manufacturing planning / engineering instructions to-the-letter, then the ball was dropped in error handling when the engineering instructions did not match the airplane configuration, because Boeing was using two different systems of record for error handling that did not communicate with each other except though manual coordination.
That's not the fault of the front-line assembly worker not following a checklist.