Never paid that close attention back then. Was only 22-23 when I started ND just wanted miles. Most trucks I drove all had 13's. Had one old Mack that was a 5x4. That was a trip. Learned my hatred for straight pipes on that truck. Cut off for grain hauling like 10-12" above the door.
I used to have a link to the eaton website that broke Down the transmission model and what it all means. Good luck finding it. They changed the website and it's not where it used to be.
I know between a 1650 vs 2050 13 spd transmission, the difference by BOM build sheet is not significant. Namely TIN plated gears. Otherwise all the bearings, clutches, shafts etc are all the same part numbers.
One of the things I dug deep into when I turned my truck up from 1650 torque to 2300 lb/ft torque.