With the prohibition era licencing police and restrictions we have in Sydney now it honestly wouldn't surprise me if clubs are deliberately under-counting to save on security costs.
Take a look at the stories around music festivals lately. The cops can charge whatever they like for security, determined by arbitrary numbers and conditions that they impose.
Hypethetically if the clubs under-report numbers, they save money on security, they still get the ticket sales, and who's gonna prove them wrong?
The only reason they may not be, I'm not sure how they'd go about it in a way that easily isn't audited should Gladys' gestapo become interested. Ticket sales and gate entries would be tracked at least semi-independently.