When using TurboTax to prepare an amendment you must print and mail the amendment. TurboTax doesn't know if you are simply correcting an incorrect originally filed Form 8606 or you did the recharacterization after April 17, 2018, so it's up to you to write "Filed pursuant to section 301.9100-2” on the amended return if it's needed.
In the case of where the 8606 was not originally filed, but the recharacterization happened before April 17, 2018- would the amendment still be required and if so- would the "Filed pursuant to section 301.9100-2 apply- since the return itself was filed correctly and the re-characterization itself was done prior to the time limit ? Even with the 8606 missing?
Assume 1099-R doesn't get released for 2017 until much later in 2018.
Section 301.9100-2 allows a 6-month extension of the April 17, 2018 deadline for recharacterizations as long as you filed by April 17, 2018. If the recharacterization occurred before April 17, 2018, section 301.9100-2 doesn't really apply, but it probably wouldn't hurt to include it as long as you filed your 2017 tax return by April 17.