Although [Seven Star Springs] was a complete technique, it was also a very old technique that hadn't been updated in a long time. After all, its requirements were basically impossible for normal cultivators to achieve, and thus when Di Tou had bought it, it had been classified as a Mid-tier Heaven Grade technique. If it was easier to cultivate, it probably wasn't something Di Tou could have even gotten his hands on, at the very least not until he got a higher tier membership at Thousand Li Stroke.
But, because it was an old technique, although all of the theories were sound, some aspects… hadn't been updated in a few thousand years, and at the same time, no one had cultivated it to a high level for a few thousand years, so these flaws were never found. In a way, this could be considered negligence on Thousand Li Stroke's part, but who could blame them?
