If you want to get technical, since Swordfell was born on a Guile's breast, doesn't that mean anything held by Swordfell is technically held by a Lurian? Because God knows Bowie wasn't the founder of the Kingdom, nor ever a Duke nearby.
Sevastian on the other hand...Has held two crowns, and held his Duchy for damn near a full RL year...Hmmmmm...
To quote Stabbity, (who just so happens to be mah wife IG)
"Lands, please."
If you want to go that far, Bowie was the Duke of Flowrestown and ruler of Aquilegia (for a day) years before Sevastian ever set foot in Central Toprak. I have more seeds spread across this part of Toprak than anywhere else.
May I say, bam.
Not to mention that Swordfell is a cooperative effort by a great many more nobles than just Bowie.