They must have a variety of sourcing for the custom work. I ordered some custom Atlas 90T hoppers in BN with FW&D and C&S reporting marks and they seriously looked like 2-year-olds did the work. I'm guessing they must have some very old pad printer laying around and they just try to eek out another few years out of it. I would be ticked if I was Atlas.
Not sure what you mean by sourcing. I think they did all the work in house. They let me tour the Anaheim shop once. But, they were known to buy the work of others and resell it. I saw them do this many times at train shows in So Cal. Not sure why the left SoCal, other than crazy house prices, to move to model train nowhere?
Some shops did carry the "primer editions" freight cars that FY painted and printed. IMO, only one or two would ever pass muster side by side with Atlas or MT.
One time I was going to have some custom locos done but the price was way to high for the quality and they dont even do number boards etc. IMO, most modelers could do better DYI.