The Calormene and Archenlanders were both in their respective lands during the rule of Jadis. Jadis only ruled Narnia (and the islands that were a part of it). As long as the humans stayed in their lands and did not stray into Narnia, Jadis had no problems with them.
If you read Horse and His Boy, you will realize that the kingdoms of Calormen and Archenland were firmly established even during the rule of Jadis. From the book:
"Know, O enlightened Prince," said the Grand Vizier, "that until the year in which your exalted father began his salutary and unending reign, the land of Narnia was covered with ice and snow and was moreover ruled by a most powerful enchantress."
They knew about Jadis because they lived in Calormen during that time. They simply knew not to go into her domain where they would have been killed.
As I said, Archenland was founded by the second son of Frank I and Helen I in about the year 30. Jadis took over in about the year 900 with her defeat and the Pevensie rule in 1000. Humans were always in Narnia (the world) and did not disappear after Jadis' rise to power.
The others I was talking about who came about 200-400 years after LWW were the Telmarine ancestors, a group of 16 humans who came into Telmar (a land west of Narnia) who eventually, led by Caspian I, invaded Narnia and took over.
MrBob