kintire said:
"By Bel, god of all thieves, I'll show them how to steal wenches: I'll have her over the Zamorian border before dawn, and there'll be a caravan waiting to receive her. Three hundred pieces of silver, a count of Ophir promised me for a sleek young Brythunian of the better class. It took me weeks, wandering among the border cities as a beggar, to find one I knew would suit. And is she a pretty baggage!"
I see your point, but I think its hardly conclusive. In that same story, Howard describes a Hyperborean renegade, a dark eyed Zamorian, a Shemitish counterfeiter, a Gunderman deserter,
and a bold eyed Brythunian.
Obviously, some parts of the known world are quite cosmopolitain. Many Brythunians are in Brythunia, but certainly not all of them.
The Kothian that said those words, boasting in a tavern, would have no way, really, of getting through the mountains in the middle of the night by dawn even if he tried. It would be mighty-slow going on a mountain trail, in the dark, even discounting all that we know lives in those mountains between Brythunia and Zamora.
Secondly is just the distance and how fast a horse can carry a human in a day. Forgetting pitch-black darkness and dangerous mountain trails, it i some distance through the mountains to Brythunia.
So, I don't take the Kothian's remark (who said that sentence above) as anything more than tavern boasting.
I hardly think it stands as proof that Arenjun and the City of Thieves are two different places.