Buy in is always conveyed by the FDA as non-objection, from the beginning to the end, but even if you get an agreement, signed by the FDA at the beginning of a trial, called an SPA (Special
Protocol Agreement), even then, they can change their mind if they decide, at the end, “You know what, those FDA guys who were here before, they were not us”.... They give no assurances that they know or will certainly do anything in the future. The risk is all on you...not them. They are not going to agree to anything that in advance that they later think, you know, we should not have agreed to that. So they never guarantee anything. Period.