I have been thinking about this for a while, and haven't really reached any conclusion, so I'll just begin.
In RGS story vol 7 on pages 399-400, there is a picture of a logging train on the New Mexico Lumber Co. showing a boxcar 3535 just behind C-16 206. It is still lettered D&RG, no W, and it is said to have been taken in '32 or '33, and the author surmises that the car was purchased by the NMLCo., but it is not so. Box 3535 went to Scenic railways, and was used as a passenger car for a time. It is now at the Rio Chama campground. I highly doubt that the D&RGW bought the car back after selling it.
This said, I would have to say that this car was the last car, or very near the last, to not have D&RGW lettering. Just an interesting thought.