I keep forgetting that you cater to the geriatric crowd. They probably don't have the energy to cheat the rotation.
That's why they all want to sing American Pie so the spotlight shines on them longer. They have to use sunscreen to protect them from the harmful rays of the stage lights.
The want to sneak in every extra minute possible...it could be their late number.
21ers to 30 are the sneaking, lying cheating age group.
It's all that untamed testosterone thing. Show offs. Look at me mom...
I had your exact scenareo tonight. 12 people in a familty get together to celebrate a wedding on saturday. They drank like fish. The "life" of the party jumped around like a nut while he sang. And he sang in several other peoples songs. The crowd actually got into him and his "style" of singing. Had several slips from them that had multiple names in different order. I used my selection method. 5 main singers in the group and the rest "helped." I had 30 singers and if they all would have stayed I would have hit 35-40. Not one person in the bar said one word about the rotation or the wedding crowd multiple singers and singing slots. Nobody got mad and left and I didn't get beat up. The wedding singers crowd didn't get mad and infact serveral of them shook my hand and introduced themselves and complimented me on my show.
I think you are way too worried about the Duet penalty clause. I'm being honest there really are not as many complaints about me rotation as you would think. The norm is not a night full of rotation beaters trying to out fox me all night.
Maybe I can get away with it because I run the music nonstop. Whenever people see Bob and Susie taking their time walking up to the designated stage area multiple times during the rotation to sing their duets and solos it gets more noticed. Since my singers are hidden in the crowd all around the bar people actually have to make an effort to see who is singing.
The one name announcement also helps. Can't blame Susie if they didn't hear her name 30 times. Once per rotation like every other singer. A girl asked me to sing with her tonight. I did and when I was done I only announced her name. But everyone knew it was her song, not mine. If it was my song and I asked someone to sing it with me I would have thanked them for helping me. So everyone knew it was my song and not hers.
It's all in how you deliver the news. Hey how come Bob is singing again? Well I only heard him say Susie's name at the end.
What is the only conclusion they can come to if they only hear one name?
That was Susies song, not Bobs. He becomes a ghost without a name.
It's karaoke not feed the world and someone took 2 life saving meals instead of one. So someone will starve to death. Get a grip. I seriously do not think thousands of singers are getting upset over someone singing a duet on someone elses slip and then them singing solo on their turn. People all can't be that stupid....let me think about that a minute..
You may as well delete your "duet" section and don't buy anymore because nobody is using it. Save the ink and paper and use thinner binders. $$$$$
About the number of microphones. I found out one important lesson about that. The more microphones being used during a "group" song, the more noise you have. Usually they are not all singing the same words at the same time. So it gets all jumbled up. I try to give them 2 microphones, three tops. That's all I use. I don't want them having anymore than that. Not because I'm cheap. If I wanted to run 20 cordless microphones I could and would. Less microphones equals less distortion during the unsyncronized singing. Too many cooks spoil the soup. To many untrained singers spoil the song mix.
The only way I shut off a microphone is if they are only screaming or they have put it down or they are not singing into it. No penalty shut down.
Handing out all those microphones give Bob that many more chances to be seen singing. The odds of him ending up with one every song is greater. Less microphones per group. 3 works good for me. I use to only use 2 for 10 years. The extra one makes it a lot nicer but that's my limit.
They are happy and the rest of the singers don't see them over doing anything. Win, win.
I "compenstate" 
for his ignorance. 
