I know what ya mean about not putting the same artist on a compilation CD twice!
Doncha hate it if you buy a compilation CD and they include more than one song by an artist?
Only way I'd put the same artist on a compilation is if its the main band & a side project or guest appearance/duet!
For instance I'd quite happily put Bon Jovi & Richie Sambora on the same CD or Winger & the duet Kip did with Fiona!