A Very Harold & Kumar 3D Christmas

We went to see A Very Harold & Kumar 3D Christmas this evening with our friends, Ray and Dawn. We got in using my blood money (movie passes from donating blood). When I tried to actually get the tickets, the lady wouldn't sell them to me because she said everyone needed to be there to show their IDs since it was rated R. What? Isn't that the point of the NC-17 rating? That only people 17 and over were allowed in? I though for R-rated movies only one person in the group had to be of age.