Britannian Succession
Prior to the rule of Charles zi Britannia, Britannia utilized a complex set of rules to determine the order of succession, which were ultimately disregarded during the succession crisis called the Emblem of Blood. Since his ascent, Charles has largely discarded former tradition in favor of doing whatever he wants. The title of (#) Prince or Princess has, therefore, essentially been a form of Imperial Family leaderboard since Charles took the throne.
Although in some cases this does appear to roughly correspond to a coherent pattern of bias related to specific consorts and the order of their birth, the death of Clovis la Britannia was very revealing: The seat of Third Prince has not been changed. This hasn't gone unnoticed among members of the Imperial Family, who perceive the vacancy as an opportunity to move up.