500 years would dilute that bloodline, iirc Royals/Nobles inbred with one another as to keep their Mana pure or something. Also Fana was a random commoner/orphan in Diamond. Dorothy could be explained as a Royal/Noble giving her to the Witch Queen to fulfill some contact or stolen by the Witch...
This still wouldn't explain it. The only friendly/neutral nation we know of it's Heart Kingdom. Also ALL reincarnated Elves where from/in Clover. Yuno being the only one that was the reincarnation of an elf and from another kingdom is too specific.
Wouldn't Yuno being Royalty from Spade be a plot hole? If I understood right, the Elves reincarnated into the descendants from the Royals/Nobles that stole their Mana?