Im sure it COULD happen and probably has at some point. Main thing is, if you have a trustworthy go to, then you will be ok. Getting random stuff from random people then you probably wont be ok, but if this was the case Id be more worried about it being something else other than an AI.
I cant really tell too much of a difference in the way I feel on the different ones (Ive used Adex, Stane, and Letro). But I can tell when Ive taken too much or too little of both Stane and Adex. I only tried Letro once, it was too strong.
OP, what does your cycle look like that you will be running the AI with? (Test dose per week and any other compounds, if any)