Because the left arm of the IRS doesn’t always communicate with its right arm, If you’re a foreign (such as Canadian) estate filing Form 1040NR and IRS issues a notice requesting USA estate Form 1041 (because although it instructs foreign estates to file 1040NR, since 1040NR is designed for use by individuals and Form 1041 is designed for use by estates, IRS will do this), then write the IRS the first letter shown in page one this PDF to receive back from IRS the second letter on same PDF page two.