When the mercenaries working for the Yuan Dynasty accosted the convoy from the Dragon Gate Courier Agency hoping to take the Dragon Sabre (which they believed was still in the possession of Mo Dong Hero # 3 Yu Doi Nam), they made a pretense of being the other six Mo Dong Heroes.
But why did they bother with such a pretense? Just *one* of the mercenaries likely would have been more powerful than agency head Do Dai Gum and his entire security staff. They could have easily overwhelmed the courier security and just taken whatever they wanted without all the complications of pretending to be the Mo Dong Heroes.
By the way, which of the mercs that turned up with Chiu Mun at Mt. Mo Dong some twenty years later were also there that day beating the stuffing out of Yu Doi Nam? Ah Dai, Ah 2, and Ah 3 were there, of course, as were the Yeun Ming Elders...but beyond that, there *had* to have been some comings and goings (i.e. deaths, resignations, firings, etc.) on the mercenary staff during the intervening two decades.