When telling Parker why they're helping him, McGee references Rules 5, 8 and 15. Gibbs' rules are: #5 You don't waste good. #8 Never take anything for granted. #15 Always work as a team.
This is the first season finale not to feature Mark Harmon as Leroy Jethro Gibbs as well as the final episode to feature Mark Harmon in the opening credits. With this episode, Season 19 is also confirmed to be the first full season with no direct reference to Anthony DiNozzo.
Jimmy is visibly limping because he is recovering from a gunshot wound to the back of his leg that he received in S19.E20 "All or Nothing".
Alden's ex-wife, Vivian Kolchak, seems to be an allusion to Kolchak: The Night Stalker (1974), a newspaper reporter that writes about macabre and unusual phenomena.
A GABA inhibitor is used treat anxiety, alcohol withdrawal, epilepsy, and to induce sedation, and anesthesia. In other words, it can place the victim in a more compliant state.