Even if the big psilocybin trial shows positive results, scientists and the FDA will likely raise specific concerns. The two main worries: first, people in the trial can usually tell whether they got the real drug (because of the obvious effects), which can skew results. Second, researchers don't yet know how long the benefits last. These are real, unresolved problems with psychedelic research, and a positive result will almost certainly spark a public debate about whether the findings hold up.
Functional unblinding and durability of effect are unresolved methodological issues in psychedelic trials; a positive readout will almost certainly draw explicit expert critique on these grounds in regulatory commentary or peer review.