As I indicated in my answer, operated properly TurboTax does carry forward the basis tracking information, even through years when no traditional IRA transactions are made. "Operated properly" means every year transferring the prior year's tax return file into current year's TurboTax to begin the current year's tax return and never telling TurboTax that you did not make nondeductible traditional IRA contributions, otherwise, as Critter#2 said, you'll need to reenter the carried-forward basis from your most recently filed Form 8606, the only thing that is needed to reenter your basis amount into TurboTax.
