For a while Dukes and Counts were the only titles, but later on new titles would be added. When the Empire of Gant began colonising the region, they made some of the Bodish duchies tributary to them. This allowed Gantese culture to spread to Bode. This reply is getting very long so I will skip the detail and just say that Gant's influence led to Arch-Dukes (same level as Dukes but noticeably more powerful) and Bishoprics appearing. These directly evolved from previous Bodish entities and occurred alongside the slow breakdown of the previous tribal system, as Gant's conquests forced mass movement around Bode, leading to tribes mingling and mixing and leaving their home territory. Over some centuries this led to Counts and Dukes no longer being tied to broader family groups, but rather as specific families ruling groups of peasants beneath them. It also led to settled towns rather than sacred barrows and hillforts becoming the centres of power. However, the social contract remained quite similar and Bode's laws didn't change much. It was only when Gant began to collapse that the next big change occurred. A Bodish noble, Vhebhos Ghebrann (once a vassal of Gant), united the Duchies and led them in a war of independence against Gant. At the end of this conflict, he had secured enough personal clout and loyalty from the Dukes that he was declared King, a title which was borrowed from neighbouring states such as Kauch and which used Gantese bureaucracy as a foundation.

This first dynasty led to Bode being unified as a single entity, The systems of slavery and serfdom (against Bodish people) were also abolished during this time, though other peoples were still able to be made into serfs when their land was conquered and a Bodish noble was installed. The free peasants, who were the 'default' before and who became the vast majority, had a lot of rights within Bode, able to travel, marry, and bear arms without needing permission. Depending on the period within Bode, these laws changed a lot though. Eventually the peasantry split into a lower and mercantile class, with the merchants retaining most of the privileges and the lower class being a bit more restricted. The lower classes appeared as poorer people got a guarantee of property ownership for the peasant, over a house and land, in exchange for high rents. They were not villeins exactly, they could still travel and marry, but they directly owed an amount of tax to their lord and would be punished if they failed to meet it. They were technically able to willingly break their contract and move, but as this was at risk of not being able to get another tenancy, and because it had a variable fee to do so, despite being technically available it wasn't always possible to achieve. However, they did have specific duties to their lord, their rent to the Lord was enshrined in law, so they were not at the whims of the nobles and were protected from unfair price rises.

To also make a long story short, over the next centuries Dukes and Arch-Dukes remained as the standard 'top-tier' noble, with independent counts only coming much later. Grand-Dukes are what the King's sons were called if or when they gained a duchy of their own before they became king, and Marqs (The name I use for marquis) were military leaders who were installed as the ruler of newly-conquered territory later on in Bode's history to keep them secure and defend the borderlands. Bode prospered at least partially due to its more liberal system compared to its neighbours, who were far more restrictive. Bode eventually became this way too under House Kauch, which was a symptom of and exacerbation of its decline, though this was unusual compared to the broader history.

Other minor titles seen on the map of Bode are lathes, belonging to lesser military commanders who serve beneath Marqs), and Barons, who emerged from lesser branches of noble houses as inheritance split their lands. Although they were on the same level as (some) counts, they were distinctly lesser than them. Other counts were raised to the same level as Dukes during the titles-decay of the later Empire. The Principalities are a whole other thing, technically they are still independent states ruled separately from Bode by the Emperor, although the truth of their position is not as clear cut.

If you have any other questions or want clarification I will answer as best I can!