You were probably born in one of the Yugoslavia(s) (the SFRJ or the later one). It's common to see "Unknown" for those who put "Yugoslavia" or similar as their country of birth. Even though the instructions now specify that the name of the country at the time of birth is the one to put in there, the "Yugoslavia" causes issues. (That's why the DoS has the opposite instruction - use the *current* name of the country. Historical names can be complicated, as you can see.) The "unknown" is not an error as far as I know and probably doesn't need to be corrected. Unless they ask you to, do not send them your GC. You can keep using it unless you have reported it lost or stolen, etc.