Ever since the covered and noncovered categories started ~2011, I've entered 3 line items per brokerage: ST covered, LT covered and LT noncovered, I confess I've never attached statements...and never had the IRS ask the client for it.  As long as the sales proceeds match (and I guess the covered basis) it was fine.

It's not as if a human looks at the attachment, if anything maybe a true or false indicator that a pdf attachment is included in the transmission?   If so, I could attach a pdf of my grocery list....(ran out of milk and eggs, busy with extensions.)