Opportunity is missed by most people because it is dressed in overalls and looks like work. - Thomas Edison
the best way that I battle this is open separation preview and click overprint preview, click off all of your spot colors (they are under the CMYK) and if you have any colors left that havent been assigned you will see them because all of your SPOTs are taken off the screen. also another easy way is to go into your print menu and select host based seps, and your spot colors should be in there and if there is any cmyk left in there the cymk tabs will still be there.. but separation preview is one of my favorites.