My recollection, tempered by age and alcohol is that the New Hartford Custom Shop was a designation that wasn't really formal until Ren showed up and the 60th was produced. As I recall Custom Shop instruments were made on the same production line using the same equipment. There may have been extra attention paid to them - I have a vague recollection of someone working on the fret board of a 60th commenting that he was being extra careful because it was as special, limited instrument. I think rosettes were done by hand on all Guilds and that would be more opportunity for special attention to detail.
I find "custom shop" is one of those terms that everyone thinks they can define but the truth is that it can't really be done without specifying a manufacturer, factory and time period. For example, some "custom shops" assembled an instrument to specifications of a player's choosing. Others made an instrument using "off the shelf" parts that were fitted, and perhaps reworked by hand. Guild's New Hartford Custom Shop had Ren involved in the design, and perhaps even in the selection of wood and modifications to "standard" parts, but Custom Shop instruments were still made by the same people, on the same production line, as regular production instruments. That said, since it is a mix of hand and machine work, I would expect people were allowed to take a little more time on the hand work to ensure that it was the best that they could do.
