Sounds like this is just an excuse to pay for the music again, and again, and again. Do club owners actually check if you have this license. And if they do, is there some requirements that they enforce the limits?

A modest proposal. If there is a limit on the amount of media on your computer, I suggest you limit yourself the the statutory maximum. Then get a large external HDD (250 GB or so) and keep it in your bag or something. Once the Music gestapo leaves plug that bad boy in and whammo, you are good to go.