My understanding as a long time experienced TurboTax (TT) users -  it is not possible to file a second return with a SAME TT log in account.   TT only allows one return being file within one log in account.     It is possible that a person could file his/her second return with a different TT account even with a same ss number.   However, IRS should reject this second filing if IRS already had 1st return registered in their system.   Just a thought.