N&W like many other RR's in the steam era tweaked their engines as any problems arose. The N&W NOT like all railroads had daily discussions with the track folks to optimize the performance of their railroad. They designed their engines for their system. N&W didn't have tons of management levels like some other roads so these discussions and teamwork in solving the problems was almost unique. Very few railroads used compound articulated engines after about 1924. The N&W liked the efficiency of their Y class and Z class (2-6-6-2) so stuck with them. Their shops were among the very best, and they designed all their Y class engines after the Y4's and built them at Roanoke Shops. N&W's profile was mostly in the hills of southwest VA and into West VA. Their flatland was from Norfolk up to Desputana or so in the east and Cincinatti eastward. That is where most of the "A" class engines worked. I will check all my books and articles to find the TE power curves and report back.