Chinese New Year, Korean Seollal, Vietnamese Tết, Tibetan Losar and Mongolian Tsagaan Sar all key off a lunar new year, and they do not reliably fall on the same day.

China and Vietnam calculate from different meridians, which is enough to put the new moon on either side of midnight in some years and split the holiday by a whole month. Tibet and Mongolia use a different calendar entirely. Calling it all 'Lunar New Year' is diplomatic, and it papers over five genuinely different pieces of arithmetic.