The single most common misunderstanding about donating a body to science is that the decision has already been made. It has not. Checking the organ donor box at the Department of Motor Vehicles registers a person as an organ and tissue donor. It does not enroll anyone in a whole-body donation program, and in many cases, the two are mutually exclusive.
Families discover this at the worst possible moment. A person dies, relatives assume a longstanding wish will be honored, and they learn within hours that no program has any record of the donor and that the window for accepting a body is short.