I have looked at it as the purpose of an AAN is to tell the customer what they need to fix to get the loan.
The agencies say that more than 4 reasons might not be helpful - I can easily understand that they could think of it as discouraging someone from reapplying.
My take is they need to know what to fix to get the loan, and although discussed by the examiners, after the explanation, they have never criticized the bank (or compliance officer).
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Integrity. With it, nothing else matters. Without it, nothing else matters.