"... if I seat each by the same amount of bullet in the case, the pressures, and therefore the load data, should be the same. "

Yep, you'd think so. There is little "standardization" in reloading data, each bullet and powder manufacturer having the own set of powder loads and COLs. Each uses different test standards, some using guns with a barrel length of "X" inches, others using test barrels of "Y" inches.

I prefer my COLs to be on the long side as long as they feed and chamber well. I haven't had any issues with them once I establish a COL that suits my firearms.