My understanding is the same as others posted above, that, given a specific type of case and bullet, the internal ballistics of your load depend more on the internal case volume where the powder burns, which changes with COAL, not case length. A longer or shorter case might affect the tension holding the bullet, but it's my guess that it's only a minor factor.
I'd also guess that using multiple headstamps and brass that varies in the times fired previously would change how the load behaves, not necessarily from differing case lengths but because of different thicknesses in the case heads changing case volume and of work hardening changing sizing and neck tension (is it still called neck tension if the cartridge isn't necked?).
ETA: I've never checked case length in 9mm, but I do sort by headstamp and times fired for ammo intended for major matches: I find ammo loaded with that brass to have more consistent velocity and to group better.