Because all of the information needed to prepare the Qualified Dividends and Capital Gain Tax Worksheet has already been provided to the IRS on line 3a of 2018 Form 1040 and, if present, line 13 of Schedule 1, lines 15 and 16 of Schedule D and line 4g of Form 4952, this worksheet never needs to be sent to the IRS. TurboTax faithfully prepares the worksheet using this same information.
As Critter suggested, I suspect that an IRS data transcriber made an error when transcribing your mailed tax return. (This generally would not be a possibility if you e-filed.)
