I.S.I.S. stands for International Secret Intelligence Service. On October 13, 2014, the creators decided to merge I.S.I.S. with the CIA for season six, due to the acronym's incidental association with the jihadist group Islamic State of Iraq and Syria, which gained attention for its violent actions in the Middle East earlier that year.
God... DAMN it, Archer!
In "El Secuestro" (Season 2), Brett's voice match on the call with the kidnappers shows his full name as "Brett Buckley." In "White Elephant"(Season 5), Brett's last name is stated by the FBI as "Bunson," causing Archer to remember the Muppet character Bunsen Honeydew.