I'm pretty sure that AIM can't be all "SO AND SO HAS POSITIVE TEST!" 'cos it's
illegal.
And, frankly, that's not the point of AIM as I understand it - the goal is to make sure that all performers have access to regular testing so when they show up at a shoot, they have the most current available tests to prevent an epidemic-level spread where possible.
Having said that, no tests are foolproof, and when one uses one's body as one's livelihood, there are levels of wear and tear one will expect - and part of that will be the fact that a performer can be carrying HIV without being positive on certain tests and a scene partner always has the potential to be at risk.