Sounds like the home was the NRA's primary resident prior to moving away from the US.

@Tex Thex CPA There's nothing that precludes the NRA from claiming §121 so long as all the conditions are met like Bob said.  I am just surprised that this is brought up only now because your client would normally have been subject to FIRPTA at the time of sale (although limited exceptions may apply) and any application for withholding reduction/exemption must be submitted to the IRS within a narrow time frame.