We just record the fact that we've tried to get in touch with the customer and have not heard back from them and consider the application withdrawn.
My only concern about using the AAN is that, on ours, we only have two options: that the "following information is needed to make a decision" or that we "are unable to approve the requrest." Since we have approved the request, neither of those check boxes makes sense.
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I hear and I forget. I see and I remember. I do and I understand.--Confucius