I think I got my terminology mixed up somewhat. The 6K was contributed to a traditional IRA with my advisor, which was combined with the (X+Y) amount from the other IRA rollover. That advisor's traditional IRA was then fully converted to a backdoor Roth. I have 5498 forms tracking the 6K contribution and the distribution from the full Roth IRA conversion. Also have the 8606 form from 2008 tracking the basis (X) for the original IRA. I assumed an 8606 for the 6K would be generated for 2021 tax year.
Not sure why the 6K wouldn't count as non-taxable in that scenario. Everything that was converted to the backdoor Roth was post tax money aside from the market gains the first traditional IRA made over those 13 years. From what I understand, that tax liability would be calculated at the time of the Roth IRA conversion.
