Oddly, it took months before I realised it was in 7/8 - I'd simply been playing what I heard on the original track and the guitarist was playing it right, it hadn't clicked that it didn't quite fit into normal length bars.
I was in a club band which went out in various forms, sometimes the guitarist was the singer and other times we had a singer. He could hit the right notes, in the right order, but song structures were a bit of a mystery to him, so the rest of us were quite adept at following him into a verse where there should have been a chorus, or vice versa, or bringing the vocals in seven bars into a 12-bar guitar solo. Still, that wasn't permanent structure changes, they were very very temporary.