Special rules

A deceased spousal unused exclusion amount may not be taken into account by a surviving spouse under paragraph (2) unless the executor of the estate of the deceased spouse files an estate tax return on which such amount is computed and makes an election on such return that such amount may be so taken into account. Such election, once made, shall be irrevocable. No election may be made under this subparagraph if such return is filed after the time prescribed by law (including extensions) for filing such return.

Notwithstanding any period of limitation in section 6501, after the time has expired under section 6501 within which a tax may be assessed under chapter 11 or 12 with respect to a deceased spousal unused exclusion amount, the Secretary may examine a return of the deceased spouse to make determinations with respect to such amount for purposes of carrying out this subsection.