Worry/Concern about 72 Hour Situation

Hi. I already I know I'm eligible for the 72 hour free Transit, as I'm flying from Russia to Hong Kong with a 12 hour layover in Beijing.

My concern/worry is, I've read articles where passengers weren't allowed to board the flight to China because the airline had never heard of the 72 Hour Free Transit policy, and denied them on board the airplane because they had no visa. I would hate for this situation to happen to me.

Is there a way that I could get some paperwork beforehand, either via the Chinese consulate or the airline company, that I could use in case this situation happens to me? Basically I'd like to get approval for the 72 Hour free transit, before I land in Beijing.

Any help would be appreciated.