User blog comment:SlyCooperFan1/Falken Factory?/@comment-4503347-20120805141203

While not necessarily reliable, Japanese wikipedia states that Grunder Industries (more specifically the Gray Men?) secretly gave the FALKEN's plans to Yuktobania so that they can produce it, with various parts produced or stored in different plants, like how Eurofighter Typhoon is in real life. Given the nature of the facility in 12B, it can be assumed that the final assembly of the aircraft takes place there.

On an interesting note, the Japanese wikipedia also states that Yuktobania fields X-02 in combat, but it was never encountered by the player (Wardog/Razgriz) during the course of the war.