Having been to the main AIM office, more than once, and had the opportunity to talk to the techs and 'talent' (porn workers), the testing doesn't stop STD's, it just lets them be treated faster. Most get something every couple of months that needs treatment.
We go and get tested and test negative every few months. With no symptoms, last time we waited a whole year. Still negative
We don't show our 'papers' and don't expect others to. We know the risks and agree to them. Just like a recent mountain climbing expedition lost people, we do what we want for fun and accept risk.
When we first started we considered a club we saw that wanted new members to be exclusive and only play within that group and to have testing. Sadly, we figure if people cheat on a spouse, why wouldn't they cheat on a sex group?