Ok thanks. I wish the header page, that Turbotax printed out with the Form 8453, explained it as well as you did.
BTW, do you know if I had opted to import the 1099-B from the brokerage (Northwestern Mutual) instead of entering the summaries by hand, would it have listed all the individual transactions and absolved me of needing to file Form 8453 ? Or does it just mean I could've mailed in the Forms 8949 with the detailed transactions instead of having to mail in the 1099-B ?
