To add key stages of applications as Layer Comps first make your changes then afterwards hit the Create new Layer Comp button (foot of Layer Comps panel). You can make further amendments, but just make sure to select Update Layer Comp to make this stick.
If you’re collaborating on an artwork and want to flag important change then the Notes Panel is paired with Layer Comps – makes sense. Simply select the Notes tool (from Eyedropper drop options in the Tool Bar). Add to the image area you want to flag and start typing what you recommend.
So you client doesn’t have Photoshop CS6. That can be a real spanner in the works. But Adobe has offered ways around such an issue. Simply select File>Scripts command. From these option you can