They should already know - I recall that Tesla "unlocked" the range a few years ago to aid people who were evacuating to avoid Hurricane Irma in Florida, and has probably done so a few times since in similar circumstances.
In fact most automotive battery packs don't use the whole battery, and most manufacturers advertise the capacity and the usable capacity - although 20%-25% is a bit excessive. Most that I'm aware of have a 2-3kWh buffer (possibly also as a redundancy); even the 120kWh Mercedes EQS has a 118kWh usable pack, and the 77.4kWh Kia EV6 is 74kWh usable.
Although I bet VW and BMW are kicking themselves now that they didn't think to hold 20kWh of capacity away and sell it back on subscription.
