Flying from South Korea to Canada.

I’m heading home to Canada at the end of August. I am currently in Korea on a working visa. I am aware that I must have at least 6 months on left on my Korean working visa in order to qualify for a Chinese travel type. I was wondering if this 6 month rule also applies to a Chinese transit type. Also, do I have to present former Chinese transit type to a customs/border agent in order to take advantage of a new transit? I went to Sri Lank in February, and I had to stop in Shanghai. Shortly after that trip, I lost my old passport.