Today my band was practicing Herbie Hancocks Chameleon, we found however that it sounded better playing Bb7 and Eb7 than Bbm7 and Eb7 (what it says on the lead sheet), this kind of makes more sense as the key signature is Bb, not Bbm. Are we playing it right (it sounds right to me) and our sheet is wrong? Or is it the other way round? Also, if it is supposed to be a Bbm7 then why is the key sig Bb, and would you play a major or minor scale off the tonic? Thanks.