Mo Wuji did not guess wrongly; he was allowed to exchange spiritual herbs. Moreover the disciple at the spiritual herbs warehouse was startled when he saw Mo Wuji, so Mo Wuji was easily able to exchange for the herbs he wanted. In addition to what he already had, Mo Wuji had gathered a total of spiritual herbs enough for 11 batches of Spirit Strengthening Pills.
With 11 batches at hand, Mo Wuji did not immediately rush into concocted pills. Instead, he went to accept a large amounts of Tier 2 Pill Refinement Tasks. After all, he was only a Tier 2 pill refiner, and his experience with concocting Tier 2 spiritual pills was limited. If he wanted to concoct Tier 3 pills, he needed to move one step at a time. Through concocting Tier 2 spiritual pills, he would be able to improve his capabilities in the shortest period of time.