As I have stated in previous occasions, I support fully the idea that there are indetermined other continents in the TSP worlds, that should be left deilberately vague so they can be used when needed. Since creating a shared, full background for the TSP that would explain where all the languages, religions etc. came from is a mammoth job that I don't believe can ever be done, having this external places of origin somewhere outside the TSP would be the best solution. 

Maybe we could agree on vague superpowers (political or cultural) that mirrors the one in the real world. So there would be (or have been) an Austral Empire to be the equivalent of the British one, an Iberian Empire for the Spanish one and so on.