Entered properly into 2010 TurboTax and carried forward each year by transferring in the previous year's tax file to begin your next tax return, this basis should already appear in your cumulative pre-2016 basis in taxable and nontaxable conversions, not as Roth contribution basis (although both are treated the same). If you don't see it reflected in your pre-2016 conversion basis, put it there rather than as contribution basis.
