I have tried to make some sense out of the information on Parker Bros. hang tags but I have so few data points it probably isn't meaningful. Generally for 12-gauge guns it appears that if they targeted the gun with 1 1/8 ounce loads they say use 2 5/8 inch shells,
211184 12-gauge, 2 5-8 inch, 1 1-8 ounce.jpg
but if they targeted the gun with 1 1/4 ounce loads the tag says use 2 3/4 inch shell.
216599 12-gauge, 2 3-4 inch, 1 1-4 ounce.jpg
All data points don't fit this. It is very general.
By Remington era the hang tags are pretty general --
240647 12-gauge, 2 3-4 inch.jpg
Parker Bros. certainly was no where near as consistent as Remington Arms Co. was with the loads used to target their hammerless double. Always UMC Load No. 8.