Aircraft registration is unique to each aircraft. Each one begins with country code follow by numbers or characters. However wikipedia says that Taiwan and China both use prefix B. So who actually own the right to use prefix B? If two of them do not co-ordinate the use of prefix them there can be two planes of same registration in the sky. So how things work out here.
https://en.wikipedia.org/wiki/Aircraft_registration https://en.wikipedia.org/wiki/List_of_aircraft_registration_prefixes