Distinguished SOTW Member, Forum Contributor 2016
I dig this.In this situation I would simply say "since charts with specific backgrounds have not been provided I'll do my thing for backgrounds and stay out of the way. Any problem with that?".
Or if one were a bit devilish, just don't say anything and when rehearsal comes, just do it the way your band has prepared it (but honestly prepare something). If, face-to-face, the artist takes issue, then explain "you only provided us with a recording and a chart/charts which didn't match ~ so left it to us how to interpret what you wanted. So..what would you like ?"
Could make for an interesting rehearsal. Might send an interesting message to the artist, in realtime.
(Then again, maybe more trouble than it is worth...)