Jin Yong is not known for going into lengthy descriptions of how his characters were dressed (which is probably one reason why the costumes vary so greatly from adaptation to adaptation), but one thing we know is this: at some point in LEGEND OF THE CONDOR HEROES, Gwok Jing stopped wearing the traditional Mongolian clothing he had worn during his upbringing in Mongolia and began to wear the Chinese style of clothing suitable for young Chinese men at the time.
The question is when did he make the fashion change? In LOCH '82 (TVB), Gwok Jing left Mongolia still wearing the Mongolian garb, but had exchanged it for Chinese-style clothing before even crossing the Great Wall into China proper (i.e. prior to separating from his Gong Nam 6 Freaks teachers and meeting Wong Yung). In one of the best LOCH comics adaptations (Ming Ho Publications, 1999-2001), however, Gwok Jing continued to wear the Mongolian clothing through the suicides of Yeung Teet Sum and Pau Sik Yerk. It wasn't until just before he and Wong Yung met North Beggar Hung 7 Gung for the first time that Gwok Jing finally ditched the Mongolian clothing and began dressing in Chinese clothing.
Did the novel specify at what point he made the switch?