Hard to say without knowing the IRS’ match up procedures. I have always suspected that it is not functional, and I cannot recall anyone reporting that the IRS’ challenged the basis amount shown on Form 8606 whether filed with the return or many years thereafter. That is odd, considering that so many taxpayers fail to file the form at all when they make a ND contribution or may not pick up the correct amount from line 14 of the prior 8606. The IRS also does not seem to inquire about TIRA contributions that are neither deducted or reported as non deductible.
If an 8606 is filed prior to the return, it is not clear what happens if an 8606 is required for another reason with the return, eg a distribution, conversion or Roth distribution. Will the IRS attempt to match up the pre filed 8606 with the return and retain both forms or will they treat the form filed with the return as the correct one?
Therefore, there may be unintended consequences for pre filing, and that in turn depends on whether the IRS will ever apply scrutiny to IRA basis issues and divert from the current honor system be used for IRA basis.
With the Secure Act provisions likely to be enacted tomorrow for 2020 and beyond, more taxpayers will be filing 8606 since the back door Roth will be available without age limit as long as there is earned income to support ND contributions.
Finally, I have never heard of anyone filing the form to report current year activity prior to the return itself, so it remains to be seen if doing so is a benefit or a problem. Probably neither if the IRS remains on the honor system when it comes to TIRA basis.