I never had to provide any part of ssn. My only action was to forward the correspondence from IRS to my escrow/title company. It was Marcelo at Mason. He took care of everything else. All he had to do was verify the money was sent and accepted by the IRS.
He mentioned that the notices were due to poor internal process at IRS. There is/was a backlog of processing the withholding. The length of the processing delay triggered notices to be sent to the buyers. There was nothing to do except to wait for the IRS to process the payment.
It might be scary, but it is normal. Nothing to worry about or avoid so long as you have a competent escrow/title company.
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