I'm late to the party, but I'd like to add the perspective of a "suit" who has been on both side of similar situations (producer and customer) a few times in my career. (Also a confirmed Demingite!)
FIRST: OP "assumes" operator either deliberately made NC parts or she took "naturally occurring" NC parts from her shift production.
(Defense says, "Once my client left Quality dept,. she no longer felt responsibility to do more than a cursory "eyeball" and being new to operating, she missed some subtle differences. Therefore, "human error.")
(I SUSPECT THIS MAY BE THE REASON NO PROSECUTION WAS SOUGHT - I KNOW LAWYERS WHO WOULD LOVE TO SUE FOR "MALICIOUS PERSECUTION AND PROSECUTION.")
SECOND: OP talks about "truth," but all I see is suspicion, no in-depth investigation to even justify "circumstantial evidence."
(HOW IN HECK DOES THE PROCESS ALLOW SUCH NC? DOES OPERATOR ALSO HAVE TO SABOTAGE THE PROCESS TO MAKE NC?)
As the suit buying the parts, my concern is how the NC were produced, not how they were packed and shipped. "You can't inspect Quality into a process."
THIRD: OP writes as if the entire burden is on OP's shoulders. Communication between the suits and the production staff is essential. a wrong move or statement could result in lawsuit or loss of the customer. This is not merely an ethical question, it is a legal and marketing one as well. Reputations are on the line and financial consequences could be huge.
An aside: nice to see some familiar names from the early days of the Cove are still around and contributing knowledge, experience, and opinions.