Ok, Bingo! The light went on, I finally understand what both of you have been asking me (for the past two days)!  I did some further investigating with the client.  There WAS a distribution from the 401k in which a 1099R was issued which I do not have in my possession  yet.  Then that distribution was used to fund the Traditional IRA which was immediately converted to Roth IRA. So you are correct, no taxable event regarding the back door, pro rata calculation is moot, not relevant.  The distribution from the 401K will be taxed. And it does not matter that the traditional IRA was funded by dollars from the 401k disbursement, he could have used any of his "already been taxed" dollars to fund it. So, yes the non deductible IRA  certainly  has full basis. I thank you for taking the time and asking me the same question in so many different ways, but the ham sandwich analogy made me a bit hungry.