The only reason they would use single stage is to cut down on time and prep work. I painted all of my car with base clear, basecoat and cleared the engine compartment first, basecoat and cleared the jambs and undersides of all panels, basecoated the outsides of panels and body, then assembled all panels on the car, back taped all the jams then basecoatef the outside of car from fender to the end of quarter panel rather than panel painting, then shot 5 coats of clear. I painted the car in my garage and the total process took me 4 days and that was working probably 16 hr days, one of the days I spent almost 8 hrs just back taping the jambs so the wouldnt be any tape lines, it was a ton of work to get it done (so much that I havent painted another car in more than 5 yrs) but the end result came out great, out of the few big shows I have taken it to be judged I have won at almost all of them but my most proud award was a best show for paint. I guess what im getting to is to make money doing restoration work affordably its cuts alot of time using single stage the way they do and im sure it looks fine, im not sure about the reputation of GYC but it looks like they do a pretty nice job to me.