There are several scenarios where TurboTax puts the user-provided taxable amount into an otherwise blank box 2a when box 2b Taxable amount not determined is marked. If the form shows no tax withholding, the e-filed tax return does not include the user-entered details of the form, so the IRS will be unaware of the change to box 2a. If there is tax withholding in box 4, the details are included in the e-filing, but I haven't seen any posts that suggest that the IRS looks at anything other than the amount in box 4. Still, whenever the taxable amount is user-supplied, be prepared with documentation to support the user-supplied taxable amount in case the IRS questions it.
