Interesting ARD stuff! Although, those don't explain the improvements in recent years. Nonetheless important to realize that with AICAR there are so many substitutes which are not covered or can't be found in tests... That testing is quite meaningless. Not a stretch there are various others that it applies to, including something in recent years. It's getting more spread across teams (as did EPO) but what it is... And if there really is such a a thing. No idea!
I'm not sure there's is a need to go for AICAR substitutes, "standard" AICAR is endogenous, so there are limitations on our ability to test for it.
It's "easy" to detect with an isotopic ratio test, but that's expensive, so you end up setting up a threshold in urine above which the isotope ratio test is applied. But that threshold can't be too low, or you will end up with quite a bit of unnecessary uses of the isotopic test, much like with testosterone and the T/E ratio.
I don't kown what the threshold is nowadays, but in the 2009 reserach paper they seem to have set it at 3500ng/mg, and according to their finding the mean concentration in non doped humans is 552ng/mg, that leaves quite a bit of wiggle room...
AICAR substitutes that are not endogenous might be completely undetectable now, but once they are known and added to the prohibited list, detecting those is child's play (relatively speaking ofc), unless they are very short lived, and the athlete is then in all kind of troubles, so why risk it?
Edit: Regarding TB500 Wim Vansevenant was caught trying to source the stuff while he was the bus driver at lotto in 2011 (cough Gilbert cough) if my memory does not betray me.