The term "reported to the IRS", in this context, is equivalent to the term "Covered"--box A (short term) or box D (long term).  "Not reported to IRS" would be equivalent to "Uncovered"--box B (short term) or box E (long term).  Note that all 1099-Bs are normally reported to the IRS.  So the choice, such at Box F, would be used for transactions, such as a house sale, where you don't have any 1099-B.