A century passed between the end of the events depicted in DGSD and the beginning of the events depicted in LOCH. From what has been written about that period, it was a very eventful era in Jin Yong's wulin, despite no novel actually depicting the events that occurred during that century.
We know that over the course of that century, the following events happened:
Deun Yu sired a son, who would in turn sire another son who would become South Emperor Deun Chi Hing. Somehow, the art of 6 Mak Divine Sword was lost during this time because neither Deun Chi Hing nor his students ever demonstrated 6 Mak Divine Swords during LOCH or ROCH.
The Beggar's Union recovered from the loss of Kiu Fung as their Chief and the controversy that it created, and eventually entered a new era of dominance under the leadership of North Beggar Hung 7 Gung.
The Shaolin Temple endured the Fireworker Monk Incident, which caused a schism within Shaolin that essentially removed Shaolin as a major presence in wulin for the better part of a century.
Wong Seung created the 9 Yum Jen Ging. At perhaps around the same time, an imperial eunuch created the Qwai Fa Bo Deen (which would not emerge during the CONDOR HEROES TRILOGY, but would come up big during SMILING PROUD WANDERER). Some years later, a monk would create the 9 Yeung Jen Ging in response to the 9 Yum Jen Ging. These new martial arts were created during the era between DGSD and LOCH, but other arts such as the Siu Yiu Sect's martial arts disappeared from wulin during this time. A few would reemerge in the timeframe of SPW in modified form. Additionally, Wong Seung's encounter with the Ming Cult brought that organization into contact with the Chinese wulin for the first (known) time.
Dook Goo Kau Bai roamed wulin and created his swordmanship philosophy, which Yeung Gor, Fung Ching Yeung, and Ling Wu Chung would utilize in various forms in the coming centuries.
Central Divinity Wong Chung Yeung won the First Mt. Hua Sword Tournament, establishing his own name and those of the other Greats. At around the same time, Lam Chiu Ying founded the Ancient Tomb Sect and established its martial arts system.
On the political front, the Khitan Liao Empire fell and was replaced by the even more powerful Jurchen Jin Empire. Dali Kingdom, Tubo Kingdom, and Hsi-Hsia Kingdom survived, but were mostly irrelevant to the story of LOCH.
All in all, a very eventful century in Jin Yong's world, but one that was never chronicled in great detail.