[StainlessSteelCynic]

Promotion to higher rank is handled quite differently in a number of other nations. For example, in many British Commonwealth/former Commonwealth nations, promotion is subject to positions being available. You may qualify for promotion, you may even attend to the courses to train you for that new rank and you may even end up taking on the responsibilities of that new rank but unless there is a vacancy you will not get promoted.
Alternately, if there are many vacancies within a unit, they will sometimes push their own troops to take the promotion courses so that one of their own gets to fill the vacancy rather than bringing in a new person unfamiliar with the unit.

You could very well have Captains who are qualified for promotion to Major and work for several years as de facto Majors but are not given the rank because their are no slots available in their unit.
I specifically choose that example because the OC of my last Army Reserve unit fell into exactly that situation. As a Reserve unit, the number of personnel in the unit depends on how many people in the area are interested in joining the Reserves and unfortunately for him, the numbers declined over the years so the unit went from being an under-strength Company to an over-strength Platoon.
While he was qualified to be promoted to Major and he was expected by higher command to do the work of a Major, the unit was not large enough to justify having a Major in command.

Perhaps the Free League system is some sort of attempt to replicate that