What are we supposed to use then? That is the only figure given from a reputable source.
A visual look around the arena at how many empty seats are empty? Photographic evidence of empty seats? Public attempts by the University to beg people to come to games? It's not like anyone needs exact numbers here. You can pretty easily tell a 2/3rds full gym from a full one.
The Drake example is a great one. Imagine if I, as an Iowa State fan, tried to use the paid attendance for that game in support of our fan support. We had 56,000 people come out to watch us play Drake during a monsoon! What great fans we have! You'd have a field day of that. But when the University of Iowa is publicly begging people to come we're all the sudden going by paid attendance?