Interesting... I have another question: my Form 8949 includes only one transaction with the M code (a $3 "Box B" short term transaction that wasn't reported to the IRS). On the back of Form 8949 there are two reported long term transactions (without code M). However, I summarized a large number of reported transactions in my tax return (Box A or D - Short or Long Term transactions that have been reported to the IRS): they are listed in the Schedule D (lines 1a, 8a and 8b) but not in the Form 8949. With the Form 8453, do I need to send the 1099B only for the "Box B unreported transaction" that has a code M, or do I need to send also the 1099-B's that include all the other reported transactions?
