Are encores at concerts getting too rehearsed?

I work as a stagehand at a concert venue, and yes, the encores are rehearsed. They are a part of the set list. There is an 11 PM noise curfew; the fine starts at $10,000 and multiplies every 5 minutes a band plays past the time limit, so it is crucial to maintain a tight schedule, therefore the encores are figured in. Many artists do the same encore every year. For example, Def Leppard always does Pour Some Sugar On Me. When we're standing by on load-out call, and we hear them break into that song, it's a signal they're coming off and get ready to jump into action to break their equipment down.