In refference to Guerreiro's case, i can only mention what was/is happening with Macedonian basketball team and few more NT's in Europe.
During the last 5 years they had some American basketball players playing for their NT. Most of these guys were african americans and they obviously had nothing to do with the Balkan.
This isn't so strange but it becomes strange when you hear how the first time in their lives these guys passed the Macedonian border was when they went there to pick up their passports, 2 or 3 days before Macedonia played a qualification match for the Euros.
Basially what happened is this :
Macedonian NT representative saw the American guy playing basketball in some european league, he asks him if he's interested to play for the Macedonian NT, the American guy hears the name Macedonia for the first time in his life but still says yes, after 2 days he gets his new passport and after 5 days he starts playing for Macedonia.