* In Season 7, Shelia "convinces" the guys at HQ to put Tommy back on duty by revealing that Mike hooked up with one of their men after-hours there, and revealing that said hookup has booze and handcuffs in his desk. How did they pull that off without getting Mike fired too, considering that she mentioned Mike ''by his full name'' during that scene? I would've expected something to happen to him as a result, officially or otherwise.
* Is it ever mentioned what happened to Chief Perolli? Feinberg's introduction implies he's Reilly's replacement, but Feinberg is usually shown in the office while Needles accompanies the crew as often as Reilly did.
* Why after Season 3 James McCaffrey continued being part of the main cast but received no billing?