I believe the Hmong "northern origin" originated from Han Chinese migrating south and mixing/assimilating with the Yangtze River native, thus Hmong people begin adopting the idea of a northern origin.
Nobody trusts oral history except when that is where the clues begin.
It was long thought that the Shang Dynasty (predecessor of the Zhou) came into being when they overthrew the Xia Dynasty (ancestors of the Han.) The Xia were merely a myth according to both western and chinese scholars. However they've uncovered relics and architecture that proves their legitimacy.
https://thediplomat.com/2016/08/revealed-the-truth-about-chinas-legendary-xia-dynasty/They also uncovered the great canal that Yu the Engineer had built (first emperor of the Xia.) The Xia once had a rival, the Jui Li Kingdom (the Nine Li tribes) ruled under the king Chi-You. After the Xia united with another kingdom did they topple the Jui Li Kingdom and slew Chi-You. The people of the Jui Li fled south to the San Miao tribes and become one people.
Nevermind the spelling, focus on the pronunciation. In Mandarin Jui sounds like the number nine in Hmong, Chi You sounds like Shi Yee and Xia when pronounced in Mandarin sounds close to Sia which is the Hmong word for Chinese/ Han Chinese. I find it strange that there are too many connections to be false when you put the evidence together. Both Hmong and Mandarin are Sino-tibetan languages, even sharing identical words with the very same meaning, others are closely similar only differing in pronunciation and tones but have the same meaning if measured together.
I'm not saying it's a fact but it could be a clue.
Sent from my SM-J327V using Tapatalk