Pahlava question

When I you conquer a new province as the Parthians, like Astauene, Margiane or Sogdiane (it's the case in all three of them, haven't conquered any others) , you have the option to 'build' Migration right away and a governement type building. I'm first of all wondering, is Migration meant to be an option for the Pahlava? I know they developped from a nomadic clan into a mostly sedentary society. I've tried building Migration first and I've tried building the government building first (Homeland-option). If you build Migration first, then once it is completed you have the next step available, Pastoralism and can still build a government building. If you build the Homeland government building first, then once it has finished, you lose the option to build Migration. Now I'm wondering if this is how it is supposed to be? Because, depending on what you build first, you have the option to have AND Migration/Pastoralism AND Homeland-government. If this is how it's supposed to be, then I'm also inclined to ask why Kiat and Nisa, the two starting cities of the Pahlava, don't have Pastoralism built in them, only the Homeland government building.

Yeah, pahlava are in flux a bit. We intend on making them more into a nomadic faction, but with reforms. We aren't there yet.

Sounds delicious and close to the truth. Much would be triggered I guess when conquering the province of Parthyaia, as was a cornerstone in real life for the Parni/Daha, future Parthians. Could you tell me how the system would come to work in future builds?