Two different itineraries a problem? Is this okay for 72 hours free transit?

If my flights are through multiple purchases, and therefore not all on the same itinerary, is this a problem?

For example, I will be flying from SE Asia on an airline ticket purchased through Ctrip. I will be arrive in GZ and depart from GZ and will be there for less than 72 hours. My flight out of GZ to the US (with NO other connections in China) will be on a separate United airlines itinerary.
So I have:
SE Asia > Guangzhou
and
Guangzhou > USA
Instead of:
SE Asia > Guangzhou > USA