As indicated in the comments above, you do need to actually look at the prior year tax returns you filed in order to complete this interview. The point of all these questions is that, when you receive a lump sum payment for prior years, you should never owe more tax on it than you would have paid if you had received the benefits during that prior year. There is a special form that's needed to make this determination and that's why you are being asked all these questions.
