WRONG - the practice is to rely on the most recent FDA draft guidances. You would be correct if the existing guidance for this particular disease were a FINAL guidance. But it was a draft guidance.
OK, well we are not going to agree. But, the FDA is more than capable of (ie, in no way prohibited from) approving blarcasemine for AD, should they ever actually submit an NDA.
All someone needs to do is find a case where draft guidence was used, over-riding final draft guidance. If this can be found, then it would be procedural, and satisfactorily demonstrate that draft guidance is the rule.