I had one of those gigs last night with a Tribute band and same thing, some different keys as the singer was also a dep, different arrangements,starts, endings etc.
Kept me on my toes trying to guess what and when the breaks would be and how the songs would end. The most uncomfortable was that many of the starts were different to the original records which you only discover when you start playing what you know and it turns out that they don't start like that anymore. Makes starting the next song an anxious moment. 🙂
But overall it was a nice gig.