Throughout the series some Officers are shown on both the day, evening and Night shifts in a short period of time, some even within the same day. The Baltimore police department rarely gives shift changes until the next fiscal year.
Throughout the last two seasons, Carcetti repeatedly refers to a possible gubernatorial challenge in 2008, after serving two years as Baltimore mayor. But Maryland holds gubernatorial elections in off years - 2006, 2010, etc. The new governor would have been elected the same year that Carcetti was elected mayor - 2006 - and up for re-election in four years, not two.