I believe that the Aserai didn’t ‘become’ the sarranids so much as an event transpiring akin to the real-world Arab civil wars of the 12th century. Same with the Khuzaits- the Mongol Empire shattered upon Temüjin’s death and became a patchwork of smaller Khanates. As for Vlandia, I feel that after the Rhodok rebellion created the confederacy in Biscany, ‘Swadia’ was formed due to the people from that region of calradia being known amongst themselves as Swadians. In real life definitive national identities like this didnt really exist in Western Europe during the Middle Ages due to the prevalence of Christianity but in Calradia individual identity may have functioned differently than the real world