In 1997, I had similar situation, business trip though. Only passport and AP paper are needed then. I used it to enter/leave China 3 time within 3 month. The 2nd time I had a little trouble when leaving Beijing. The boarder police thought the AP paper was too informal, just a piece of paper. They could not understand how this piece of paper could let you in US. They should not have cared about it because I have a valid passport and boarding pass. Usually it's the airline's job to ensure that you have proper entry documents. He had to get his supervisor come and they spent about 10 minutes to figure out it's OK and let me go.