Sorry folks - don't understand this 'only on guest nights' bit.
As far as I'm concerned a club should stand and fall by its regular singers - they are the constants who shape the club and set the standards (or not, as the case may be) and it is in their hands that the club/revival/music will stand or fall.
Wouldn't dream of asking a guest not to use a crib sheet - on the other hand he/she wouldn't get a booking in any club I had anything to do with if they did.
Jim Carroll