Many who raised similar questions in the past had assumed backdoor conversion is a tax-free transaction.  It is not.

Even if the taxpayer had only one brand new IRA account, made nondeductible contribution, and immediately converted the IRA to ROTH with no earnings or loss, there is no taxable income from the conversion not because it's not taxable but only because there is no taxable income to recognize.

And even if the taxpayer is converting an amount below the basis in the IRA, the taxpayer still cannot treat the conversion as coming only from the basis.