While important and accurate, Arduin deviated in some interesting ways from perhaps the normal. Which is a expected event, given their style of government, while parallel to feudalism in our own world did not evolve exactly the same
It grew in starts and fits out of the provisional government set up after the Accords of Arduin, and was guided by those leaders who drew upon their own experience with the governments they grew up with and had just renounced allegiance to, in order to make the covenant of peace work.
The standard practice of a noble or individual receiving a land grant in exchange for their contribution of troops to the crown’s army did not spur the creation of the noble ranks (at least initially).
The Accords of Arduin had made it abundantly plain that each nation that filled the Plains of Paranon that day of peace would provide a number of troops, as well as settlers, that would renounce their former heritage to take on another.
The provisional governor, when it all finished, ended up with a large number of settlers, and an equally large amount of soldiers. These soldiers, however, were only nominally under his command as each arrived with its own commander, with his or her own agendas set forth by their parent nation.
I won’t go into the dance of politics that was required to weld this into a working provisional government and later into a kingdom (though its included in the world book).
What I will say is in the current structure of the kingdom the noble ranks are very much as outlined in AG II, at least for the nation of Arduin. There are Archdukes, Dukes, Barons, Marquis, Viscounts, and Counts—these are the landed high noble families of the Arduin nation. These are all covered in great detail in the world book of khaas, as are their associated families, demesnes and so forth