不知道是不是跟这有关？
https://goo.gl/jFojSb
台湾关系法:
至于移民及国籍法方面，应根据该法202项(b)款规定对待台湾
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.