"I received 1099-INVs for the distributions from the traditional to fund the Roth conversions."
This would have been reported on a Form 1099-R. There is no such thing as a 1099-INV.
If you used TurboTax to prepare your 2018 tax return which, properly prepared, would have included Form 8606 showing your nondeductible traditional IRA contribution having been included in the total on line 14. Transferring that tax return file into 2019 TurboTax would have transferred in this basis to show on line 2 of your 2019 Form 8606. However, if, when TurboTax asked, you inadvertently indicated that you did not make nondeductible contributions for any years proper to 2019, 2019 TurboTax would have silently deleted this information that had been carried over from your 2018 tax return.
If the basis information is still present in your 2019 tax file, you'll see it on TurboTax's IRA Information Worksheet and will also be present on Form 8606 line 2 to be used in calculating the taxable amount of your Roth conversion. Be sure to click the Continue button on the Your 1099-R Entries page to reach the questions asking you to confirm your basis and for your year-end balance in traditional IRAs. If your year-end balance in traditional IRAs was nonzero, some, perhaps a large portion, of your Roth conversion will be taxable with the inapplicable portion of your basis remaining with your traditional IRAs to be applied to future distributions, all calculated on Form 8606.
