Presumably you have no other funds in traditional IRAs since the pro rata rule treats all of your traditional IRAs in aggregate as if they are a single large traditional IRA. Because of this there is really no such thing as an "after-tax traditional IRA," only after-tax, nondeductible contributions to your traditional IRAs.
No matter what you do, Form 8606 Parts I and II are required to be included with your 2023 tax return. If you have $1 left in traditional IRAs at the end of 2023, $6,499 of your $6,500 Roth conversion will be nontaxable and $1 will be taxable. If you do noting more, $1 of basis will remain in your traditional IRA.
Opus 17 is correct. Since you presently have $1 in traditional IRAs and $1 in basis, the simplest thing to do would be to convert this remaining $1 before the end of 2023. Doing so won't change your taxable income. You would still receive a single Form 1099-R and it would report the total of $6,501 converted.
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