Unfortunately, you cannot carry forward information from 2014. TurboTax 2017 will carry-forward information only from 2016. Similarly TurboTax 2016 will carry-forward information from TurboTax 2015.

If TT2014 was used to prepare 2016 info, why does it not allow carry forward to 2017?

If your 2016 return has the 2014 info that you are talking about then, TurboTax will carry-forward your updated 2016 return but it wont carry-forward anything from 2014 directly. Technically, TurboTax will carry forward your information only from your previous year.