I haven't found any original USA document confirming or falsifying the fact that they were numbered in the same order, but I did find one photo in which you can make out the last digit of the Alco shop number, and that loco is in the same order of both the D&RGW and USA series. I have attached a portion of a print that I have of USA #256, and the last digit of the shop number is
zero (
0). That would make it Alco #68990, or D&RGW # 479. So, this loco is the highest of both the D&RGW ##470-479 series and the USA ##250-256 series.
If they numbered the USA 250 class randomly, there still is a 1/7 chance that Alco #68990 would have been USA #256, but a 6/7 chance otherwise. Maybe someone else has a photo in which you can make out the shop number of one of USA ##250-255, and that would either dramatically increase the odds above 6/7, or demonstrate that they were not in order.
Robert