If I get handed a pile of slips from one singer I play them right down the pile. If someone else gives me a slip with a song on it that was going to be the other singers next song, but their first I let the second singer sing it and change the first singers #2 song to their #3 song. No big deal. Now 99% of the time they know what happened and why. I would do it the other way around for them. Sometimes you get the bear and sometimes the bear gets you.
I will not reserve a song for anyone, period. If Bob has a song in already and Frank walks in and sings it first every night, too bad for Frank he should have been there earlier. Same would go for Bob.
It's totally impossible to make every singer happy every night. Yes they may have really wanted to sing that song, but they had a choice to make. Get there first and put it in first. Don't cry to me about it if you pussyfooted around with it and someone else sang it first.
Maybe $$$$ used to reserve a song would be a better way to go. $20 can reserve any song you want. Not a place in the rotation but a place in your pile of songs for the night. That would solve a lot of problems.
Shut up and pay. You can sing whatever you want on your turn at $20 a pop. How many will want to reserve songs then???