Which version supports previous year filings as far back as 2012?

Do you need to file old returns?  

You can only buy the download for prior years. You have to buy a separate program for each year. They only sell the last 3 years. You need a full Windows or Mac computer to install it on. Buy the download here
https://turbotax.intuit.com/personal-taxes/past-years-products/

You have to print and mail prior year returns. When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s. Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS received the return. Don’t forget state.

Important! Mail Federal and State in separate envelopes and mail each year in separate envelopes.

If you are getting a refund, there is not a penalty for filing past the deadline. You have 3 years to file for a refund. If you owe taxes, the interest/penalties will be calculated by the IRS based on how much you owe and when they receive your return and payment. The IRS will bill you for this; it will not be calculated by TurboTax.

How to file a prior year
https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-prepare-a-prior-year-tax-return/00/25984

Each tax year is a separate TurboTax program.  TurboTax supports tax years 2019 thru 2016.  The current tax year, 2019, is available from either TurboTax online editions or the desktop CD/Download editions.

Go to this TurboTax website and choose the product by clicking on Products & Pricing - https://turbotax.intuit.com/

To complete and file prior year tax returns (2018 thru 2016) using TurboTax you would need to purchase, download and install on a personal computer one of the desktop editions for each tax year needed from this website - https://turbotax.intuit.com/personal-taxes/past-years-products/

Prior year tax returns can only be printed and mailed, they cannot be e-filed.  Use separate envelopes for each tax year when mailing.