Good questions Greg - spot on. Is it too impractical to suggest that clubs might reserve a one-or-two monthly evening just for last-minute unforseen possibilities? Or maybe call it a Newcomer's & Visitors night so the established acts who have been trying for ages to get a booking (and who maybe you don't want but don't like to say) won't feel hard done by. Keep it for either foreign acts passing through (or people you don't often have a chance to see) or new talent, maybe? You could always warn your audience in advance that if no one new is around to book in a particular month, that it will be a singers night. It would probably broaden their tastes too.

Id like to hear what organisers think of this point because I really agree with Greg that the club rosters need to be more flexible and not get so locked in so tight.