We all know (or at least the ones with basic chemistry knowledge) that the whole 84% pure MDMA figure that has come to be said as the max purity that can be obtained when vendors (namely European ones) advertise their stuff is inaccurate and is only referring to the fact that any given amount of MDMA will, by mass, be 84% MDMA with the other 16% being the HCl salt it's bound to. Since the HCl is inactive, it's irrelevant to consider it as apart of the product you're getting, no one discusses their doses as being 84 mg MDMA when they take 100 mg, which is technically what they'd be getting. Is there a reason this is still a thing other than the inaccuracy somehow developed and no one knew anything different or to correct it?
This isn't a thing with any other drug that's in it's salt form like coke or anything else so it's strange that it's developed with MDMA. Kinda annoying, but am admittedly a mild chemistry nerd. Even if the vendors products are nearly top-notch purity but not 100% (rare if ever with any compound) it would still be far more accurate to range it at around 90-95%. Do we anticipate they will ever change this inaccuracy? It's not a big deal, just a slight annoyance.
It's just how things worked out. No reasoning behind it, just caught on to refer to it like that.