144-hour visa-free transit not as stated - Guangdong

TL;DR; 144-hour visa-free transit documentation is either wrong or very unclear for Guangdong and will create headaches if you don't only fly into and out of China with the program.

Just wanted to give our experience with some relatives trying to use the 144 visa-free transit scheme to visit us in Guangdong.

Plan: LAX - CAN - HKG - LAX (round trip to Hong Kong with transit via Guangzhou)

As all the documentation from the Chinese government and China Southern says 32 ports (including airports, railway ports, road ports, and sea ports) apply to exiting China, we purchased railway tickets from Guangzhou to HK Kowloon West.

Experience:

At LAX, our relatives were questioned about not having a visa and only needed to mention and show information about the scheme/program. At another airport enroute to Guangzhou, they were asked about it again and stated that the train tickets didn't apply for the onward ticket out of China. We quickly purchased bus tickets and the airline let my relatives board.

At CAN, my relatives showed the train tickets and bus tickets and the immigration officers said all of those didn't apply. They said only certain bus tickets, flight tickets, or ferry tickets apply for this program. We got around it finally by buying tickets from Nansha to HK. We were hoping to cross the boarder via car for more convenience, but are now super nervous about how strict and arbitrary China is with this 144-hour visa-free transit program.

Overall recommendation: Only book airline tickets for the onward journey OR avoid entirely.

Edit: Adding links for info about the 144-hour visa-free transit program.

https://www.csair.com/en/tourguide/transit_flow/flightsTwo_hub/72_hour_stay/

https://en.nia.gov.cn/n162/n227/c116266/content.html

http://gdga.gd.gov.cn/xxgk/zcjd/wjjd/content/post_2286867.html