If the filing threshold has been met, or in other words, if, independent of the portability election, the estate is required to file an estate tax return based on the total value of the gross estate and adjusted taxable gifts, no extension of time to elect portability is available and Revenue Procedure 2017-34 does not apply.
Verification is the process of assuring that the product satisfies the conditions before work starts. Validation is the process of assuring that the product meets the specified requirements at the end of the development phase. In other words, to make sure the product is designed in accordance with customer's requirements.
In a traditional phased software lifecycle, verification is often taken to mean checking that the products of each phase satisfy the requirements of the previous phase. Validation is relegated to just the begining and ending of the project: requirements analysis and acceptance testing.