Losar in Utsang region following new calendar introduced into Tibet from Dhenpa chidhar or after collapse of Tibetan empire. If you observe carefully Tamang losar , amdo losar and Chinese losar usually fell on same day. Tamang and amdo region never reunited into one country. During golden period of Tibetan empire whole country followed one calendar or method of astrology which was similar with Chinese astrology. That method of calendar calculation was introduced into Tibet and China from India in ancient time..
