The pro-rata rule has applied ever since nondeductible traditional IRA contributions have been permitted, more than 30 years. Because your wife' traditional IRAs have more than just basis, any distribution will be a mix a nontaxable basis and taxable amounts. She'll always have some basis in her traditional IRAs until she has no more money in traditional IRAs at year end. Whatever basis was not permitted to be included in a particular distribution will remain in her traditional IRAs to be applied to future distributions.
