Have you used the online platform for all of those years? They would only have your returns if you used TurboTax Online.
Edited to add: Most often, users who can't locate their returns used a different account to prepare those returns. Many users have more than one account and don't realize it. The TurboTax FAQ linked below may help you locate your returns.
Why can't I find my return in Tax Home or My Docs?
*** I am NOT a tax expert. I am a seasoned TurboTax user, and volunteer to provide assistance to TT users. Nothing I post is to be considered TAX ADVICE; I bear no legal liability for responses.***
