The quoted text from the IRS results from the wording in the statute that was written before the change in the law that permits IRA contributions for a particular tax year to be made by the due date of the tax return for that tax year. The wording in the statute was never updated to resolve the ambiguity and the IRS has never issued any guidance to clear up this ambiguity. That leaves it largely up to the IRA custodian to interpret the statute.
