German citizenship in the FRG is... a little tricky.

The government in Bonn claimed that the Federal Republic of Germany was the legitimate placeholder government until a final peace treaty could be conducted between the four Allied powers and Germany. In the eyes of the FRG's constitution, Basic Law, there were no two separate German states. Article 116 of Basic Law defined "German" fairly broadly both on the basis of birth within 1937 borders (ie pre-Anschluß), as well as those considered Volksdeutsche. So not only were the GDR's inhabitants considered FRG citizens, so too were ethnic German expellees under Basic Law.

West Berlin became a de facto part of West Germany, subject to Basic Law and its citizens held FRG passports, but was never an official part of the FRG. The city was technically still under Allied control until that final peace treaty. West Belriners could vote for representatives for the Bundestag, but these representatives could not vote in the chamber. But while West Berlin did not participate directly in federal democracy, the city did form a close relationship with the federal bureaucracy and the chancellery. The western half of the city also enjoyed a number of special privileges not common in the rest of the FRG. West Berlin men were not subject to conscription and Bonn doled out subsidies and tax breaks to West Berliners to prevent outflight from the city. West Berlin wags often termed these breaks Zitterpraemie (jitters premiums) given the flashpoint nature of the Cold War in West Berlin.

The Four Plus One Treaty that formally ended German division also ended West Berlin's unique status and it became a formal federal Land in 1990. But the citizenship mandates of Article 116 remain in place and this was why a number of individuals descended from Volga Germans were able to gain German citizenship after the collapse of the USSR in the 1990s.