Treasures that could raise lifespan were not common, and almost always, they were naturally occurring. It was unheard of to come across some potion, pill, or cultivation art that could do it. Of course, just because it was unheard of didn't mean such a possibility didn't exist. Cultivators were notoriously secretive about a lot of things.
The more trump cards one had hidden, the better, and having a technique, spell, potion, or pill that could extend one's lifespan definitely fell into the category of trump cards one would keep secret for as long as possible.
"Yes," Yang Qing said, nodding. "We found the sect's founder alive, and yet the records showed she was someone who should have already been dead.
