Continuity mistake: When Abby tells McGee that the suspect has a gun, there is an overhead shot of the top of the building and the brown car is at least 4 spaces away from it. When Abby is watching the report on TV and says "damn you Gibbs", the car is next to the building. (00:04:00 - 00:05:00)
Continuity mistake: When Gibbs is trying to talk Lt. Arnett out of jumping off the ledge, Gibbs is relatively close to Arnett in the middle of The Wall when Ducky and Abby watch the live news report, but in real time, Gibbs is over at the far left corner of The Wall. (00:04:10 - 00:05:00)
Continuity mistake: When the CO opens the drawer of Michael's personal effects, the items change place or change entirely between shots. For example a book appears. (00:13:05)
Continuity mistake: The pill bottle the agents recovered from the house has the Doctor's name "Fleming" to search for. But when McGee searches the NCIS system, he spells the name "Flemming" and gets his results. As well, the scrip sheets for Dr. Flemming archived on the computer, contain several identification numbers - DEA (AJ0000000000), Batch (00000001) & License (C00000.) - not real numbers - so the prop master didn't even try to fake any of them. (00:15:20)
Continuity mistake: When the shrink asks if DiNozzo and McGee are a couple, their positions change instantly. (00:18:40)
Continuity mistake: When Jenny thanks Nikki for coming in so quickly, Nikki has her coat over her hands, camera changes and now her hands are uncovered. (00:22:00)
Continuity mistake: When DiNozzo mimics sneezing on Nikki she reacts and freezes. Camera changes and her entire position has changed. (00:26:15)
Chosen answer: It is never stated, however she must have been there several years if she is on presidential detail.