Yes, if your shares were acquired before 2012, the holding period is long term. A holding period greater than one year--a year and a day--is considered long term. One year or less is considered short term.
If you don't know your cost basis, TurboTax won't be able to determine whether you have a capital gain or a capital loss. It is unlikely that the IRS will know your cost basis either. Therefore, you will need to do the research and then enter your cost basis into TurboTax. If you know, or can determine, the approximate time period when you acquired the shares, you can do an historical price search using a financial news site, such as Yahoo Finance, to get a good idea of the price you might have paid for your shares. You are correct in that if you cannot determine your cost basis, the IRS may assume it is zero, and you will pay capital gains tax on your entire proceeds from the sale. Thus, do your research and find the price you paid for the shares.
@LuongPNguyen
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