Form 8606 IRA Basis

I am using free online version. I have used downloaded versions in past. I am trying to figure out where this IRS 8606 form is getting the IRA basis from what I have told it in Form 1040. I have 1099-Rs that show these were not taxable and were rolled into a traditional IRA. I have one small recharacterization of credit card rewards from a traditional to a Roth IRA, and that apparently is prompting this form to generate? Where does it get these dollar amounts to determine a total basis for 2024 and prior years?

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