The mystery of precisely who stole the Chinese Ming Cult's Sacred Flame Tablets, which were missing for 100 years before Cheung Mo Gei found them in the possession of the Persian Ming Cult, was never resolved.
I think, however, that I might have a suspect.
According to the Chinese Ming Cult members of the HSDS era, the Sacred Flame Tablets were stolen 100 years before their time...in other words, around the time of ROCH.
ROCH featured one Persian character: the mercenary warrior Wan Hak Sai, who served the Mongol Empire under Kublai.
Why do I suspect Wan Hak Sai? Several reasons:
1. He was Persian; perhaps he was a member of the Persian Ming Cult and stole the Chinese Ming Cult's Sacred Flame Tablets in the hope that he would be rewarded by the Persian Ming Cult.
2. He was covetous. Not only was he a wealthy jewel merchant, but he coveted Yeung Gor's Heavy Iron Sword (tried unsucessfully to steal it from Yeung Gor at Chung Yeung Temple), and ultimately lost his life because he coveted the 9 Yeung Jen Ging and fought his fellow mercenary, Siu Seung Tze, to the death for it. Thus, stealing the Sacred Flame Tablets (and knowing their value, assuming that he was indeed a Persian Ming Cult member or associate) in the hope of personal gain would fit his covetous character.
Jin Yong never hinted that Wan Hak Sai stole the Sacred Flame Tablets or had any connection to the Ming Cult, but if we use a little imagination, we can see ways that such a subplot could be feasible.