When the employees end their late night work the clock reads 9:03. Then, once everyone begins to file out, the clock reads 9:00.
Since Hank sits at his desk all day, he should've known that the staff were still there.
When speaking Spanish with the cleaning staff, Oscar does so with a Cuban accent, even though he is Mexican. In real life, actor Oscar Nuñez is Cuban.
Dwight should have been able to detect Ryan's cocaine addiction.