Yes, the notice states, "If they agree, send the B notice."  The accounts did agree.  The question was still, should I contact that contractor?  The letter stated explicitly that I do not need to contact the IRS or prepare a corrected 1099.  This implies to me that they already know he gave them the wrong number.  Whether he was cheating on his taxes or not remains unknown.  It was a substantial payment.  They have his name and address, of course.  

I did not send the B notice because there will never be any future contact with him and cannot be backup withholding.