i worked at gnc in college and new supplement companies always seemed to come out of nowhere. as a supplement manufacturer, you want your customers to get the biggest gains, greatest intensity, fastest recovery, etc. the newest products always walked a fine line when it came to ban-able substances. after a couple months, the newest ingredient would make the banned substance list and they'd have to recall and re-formulate everything. lots of times there was no recall, and you could continue to buy banned supplements as long as they were available---we still sold them but we didn't get replenished.
i remember back in the day when they banned andro and ephedra and everyone wanted it after the ban.
there's no way to regulate supplements and the ban list is ever-changing. you'll always have a guy who fucks up because he took the wrong shit or even too much of the right shit. but still, as a pro-athlete, you have so many resources at your disposal that this should never happen.