Why does the AAMVA CDL Manual say that ALL students, not just the designated assistants, must know how to operate the emergency exits and must follow the driver's instructions?

AAMVA CDL Manual, Section 10.3.2 – Evacuation Procedures (Be Prepared and Plan Ahead), p. 10-6

A pre-assigned plan only works if the right students happen to be on that specific bus that day. Training every student as a backup means an evacuation can still go smoothly even when the usual helpers are absent or the emergency happens on an unexpected route.