got the R door, R fender, R rocker in primer last night. I was kind of bummed to realize I didn't even fully sand a patch of mud low on the rocker. Was planning on only priming that area once but I guess I'll have to spot some primer on the rocker later. The door and fender don't need any more primer but will let them sit and kick for a week or two. Also realized the after market L quarter that was installed had an all too common issue...the stamp caused the middle of the wheel crown to be caved in. You can't always find this with guide coat and sometimes it's hard to find with your hands so it's best to use a straight edge for this area. You really need to access this area BEFORE you put mud on it, but at the time I didn't think about it.
Moral of the story, guide coat is just part of the equation. If anything, I'd say a good hand feel and using it when needed is just as important if not more important than guide coat. If this wasn't the case then guide coat would show you everything on hoods and decklids but to get them truly straight you need to put the guide coat to the side and rub your hands all over it in multiple directions. Some guys think it's not an exact science but neither is guide coat, otherwise it would show you the hood/deck isn't straight. The best handtool is the hand itself in body work.