Yes, it makes a difference.
(1) Any sale of an inherited investment is treated as long-term, no matter how long it was actually owned by you or the person you inherited it from.
(2) It's not clear what basis the brokerage "transferred." The basis of an inherited asset is the fair market value on the date of death of the person you inherited it from. Is that what the brokerage reported on the 1099-B, or did they report the deceased person's basis?
Did the "many subsequent dividend reinvestments" occur after you inherited the investment, or before? Reinvestments that were made before the date of death don't have to be treated separately, because they all get the date-of-death value as basis.
