Enjoying this discussion, it really highlights what you can find in the clinic.
I was more wondering how you think they might do it, if they were to implement such limits. The potential to find banned substances in supplements is fairly high and there are pretty much "cheat sheets" available in the literature telling athletes what they can take and still feasibly blame it on a supplement. From your post I'm guessing you think they'd set limits for everything if they went this route and accept the possibility it allows for doping?
I'm actually not sure that WADA need to change their rules. I am interested in the liability of Informed Sport and supplement manufacturers (and I realise
@stephenm may not wish to comment around this). If an athlete were to used an Informed Sport tested product and test positive for a banned substance, who would be liable for their loss of earnings? The rules are pretty clear, strict liability means the athlete is responsible for what they consume, but do the claims from Informed Sport amount to a contract of guaranteed clean products? (Or as close to guaranteed as you can get). Does using Informed Sport to test for banned products provide some indemnity to the supplement manufacturer? If these things are true, could an athlete who can prove that the supplement they took contains a banned substance AND was accredited via Informed Sport bring a case for loss of earnings? I'm aware that the likelihood of this happening is extremely small.
Maybe an addition to the ADAMS system inline with Informed Sport is required. You log supplement batch numbers in ADAMS and in the event of a positive it can be traced back to the possibly contaminated supplement. I'm not sure on the costs etc. but it might be feasible for all batches that are sold with the Informed Sport mark to be tested, or at least stored for future testing. It doesn't alter the rules, it just provides some added security for athletes who choose to use properly tested supplements. It also highlights to those athletes who are not using tested supplements that what they are doing is not covered.
I'm guessing that SIS/Etixx/MaxiMuscle etc. probably store some of each batch for future testing, just in case an athlete tries to blame them, so an ADAMS update wouldn't actually be a huge change. It would just make it part of the monitoring system and have a process for checking put in place that all parties are aware of. It would also mean that, if a supplement were found to be contaminated, the system could be used to alert other athletes and remove it from circulation. I'm aware this only covers athletes using ADAMS, but NADOs could send out alerts too along with governing bodies.
On more of an academic point of self interest, I wonder if there is a possibility of a Diane Modahl-like situation occurring, where a supplement contains something that, upon metabolism, converts into a banned substance or creates a positive test for a naturally-occurring substance like testosterone? (I'm aware Diane's case was due to sample degradation so not the same, just similar). This wouldn't necessarily show up in testing of the supplement.