Don't sweat your scenario. Answer ALL questions HONESTLY and bring the admin letter and all supporting documents to the interview. If necessary you could also bring a letter from another member of your unit that substantiates the situation. I don't know if Airline Apps still permits an addendum but you also may be able to scan the letter and attach as a PDF document.

Because of several accidents involving pilots with poor performance history, airlines are quite sensitive to the issue. A single event, particularly caused by an admin process that is easily explained and documented, is not something that will cause any heartburn.

FWIW, the only pilot I've ever known to be fired from UAL was fired from my new hire class during indoc when UAL found out that he had answered "no" to a question that the background check returned a different result. The issue was minor but the UAL legal & HR departments would not retain a pilot that "lied" on the application. Had he answered differently the entire episode would have been a non-event.