Speaking as someone who works at the club I'd say the numbers are more like about 70% of the time cameras are not allowed while about 30% of the time they are, a far cry from 99.9%.
Each show the headliner tells us what they want the recording policy to be. Sometimes they don't want any cameras in the building, sometimes they just don't want pro cameras or digital cameras, other times they just don't want any flash photography. Some nights it's all cool. It changes night to night.
As far as knowing when you can and cannot take pictures, sometimes we don't know till just before doors what is or isn't allowed. We suggest if you want to be able to take pictures to bring your camera to the club. Before you bring it inside the building simply ask one of our friendly doorstaff if you are allowed to bring it in. We also post each shows policy right on the front door as you walk in.