My question is with the peerage chart on page 27.
Marquis and Margrave are the exact same rank in historical European nobility, the same as the German "Markgraf" and the rare English form "Marquess". All essentially mean "march count", that is, a count who is in charge of a border region or frontier (a "march"), and thus were given greater autonomy and military authority, in order to quell uprisings and more quickly react to cross-border raids, etc.
(Margravine is the female form, but it's unclear to which tier Miyabi belongs.)
Was the hiccup in the original text or in the translation?