不知道是不是跟這有關？
https://goo.gl/jFojSb
台灣關係法:
至於移民及國籍法方面，應根據該法202項(b)款規定對待臺灣
INA202(b): https://goo.gl/n12x73
(B)/othing in this paragraph shall be construed to limit the authority of the Secretary of State to determine the procedures for the processing of immigrant visa applications or the locations where such applications will be processed.