If the 1099-B shows basis was reported to the IRS and you made an adjustments in box 1f or 1g, you are required to mail in the explanation. TurboTax automatically adds the Form 8453 if you meet one of the requirements to send it. (it does not have to be an affirmative election on your part). See E-file.
You should mail the 8453 with the explanation to avoid future IRS issues.
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