IRS grants estate executors who want to claim portability up to 15 months after the decedent's death to file an estate tax return. Notice 2012-21 offers relief to estate executors who missed the deadline for filing for an automatic six-month extension to claim portability, but now want to take advantage of a deceased spouse's unused $5 million estate tax exclusion amount. The extension is likely to thrill taxpayers who were caught unaware by a new IRS portability filing requirement, practitioners tell Bloomberg BNA.