You know, it's interesting that some fans are frustrated by the large portions of Narnian/Archenlander/Calormene history that aren't explained or depicted in the books. It's possible that there were some good stories in those parts, but I feel like if there really were, C. S. Lewis would have written about them, and he didn't. I don't find political and military stuff interesting in real life, so I'm not interested in that part of Narnia. 

"I wish we had someone to tell us what all those places are," said Digory.
"I don't suppose they're anywhere yet," said Polly. "I mean, there's no one there, and nothing happening. The world only began today."
"No, but people will get there," said Digory. "And then they'll have histories, you know."
"Well, it's a jolly good thing they haven't now," said Polly. "Because nobody can be made to learn it. Battles and dates and all that rot."

I think that pretty much sums it up.  

I think what's nice about the Narnia series as a whole you get to explore other parts of the world Narnia. Given that LWW was the first book to be published, obviously, CS Lewis haven't thought of Archenland or Calormen yet.

I've always consider HHB to be more of a side book because it actually takes place during LWW. We get to see a glimpse of what's been going on during the Pevensies reign.

I'm thinking that Archenland just like simple names, even names for twins. It must have been common in that region.