"The secluded immortal sects…"
Since both the youthful guru and Elder Guo could be considered the oldest people on Earth, they definitely knew more secrets. Even so, they did not know much about the secluded immortal sects.
After all, cultivators were rarely active around the world ever since that upheaval over two thousand years ago.
That said, there were some immortal sect disciples who came out to train around a thousand years ago. Some of them practiced steeling their emotions in the mortal realm, while others obtained immortal legacies by chance and caused a major stir, leaving many legends. Even so, no immortal showed up again with the gradual drying up of Spirit Qi—how difficult was the battle around five hundred years ago without them?