If you are talking Mao from Darker Than Black, as your fourth Mao, perhaps that is a crossover that should be.
If Mao Zedong, well, I consider Chung and Halliday's Mao: The Unknown Story to be canon. I think Mao: The Unknown Story should not be crossed over with anything. Essentially, I lost the roll to disbelieve, lost the SAN, and decided I couldn't stand to read any more of it. (Or at least, the cost in depression was not worth it. I probably paid too much, and too long as it is.)
If Mao Zedong, well, I consider Chung and Halliday's Mao: The Unknown Story to be canon. I think Mao: The Unknown Story should not be crossed over with anything. Essentially, I lost the roll to disbelieve, lost the SAN, and decided I couldn't stand to read any more of it. (Or at least, the cost in depression was not worth it. I probably paid too much, and too long as it is.)