The following is just a guess, but I think I'm on the right track... after Victor Miller was replaced as the RGS Trustee, he retained many of the cars that were previously used on the Southern, however, photos show most of the stock cars remained. I think that's because there wasn't any market for used narrow gauge stock cars at that time. However, after the box cars were removed, the Southern still had need for box cars to service the many online mines, so they arranged to lease some surplus D&RGW boxcars. These I believe are the ones that only have a number. Most, if not all of the D&RGW boxcars still in service were still fully painted, which may explain the number only boxcars seen at this time, especially as you got closer to the RGS.