D&RGW Number only boxcars

There are a lot of photos taken (starting in the late 30's/early 40's) of D&RGW 3000 series boxars lettered with simply a number. Many tend to show up on photos on the RGS, but apparently they were seen all over the D&RGW lines as well. My guess is that since the lettering (white lead lettering paste) would weather faster than the car paint would, as well as various shortages during the WWII period, not all cars would get repainted as often as would have happened earlier. Coupled with the new herald (Flying Rio Grande) which appeared in 1939, I would suspect if a car lost it's lettering, and the paint was in good condition, it would simply have it's number restenceled instead of repainted. Especially if the car tended to stay on the western extremities of the system and away from the Alamosa car shops.
So my question is, is this a reasonable assumption?

Bill Daniels
Santa Rosa, California