Simply because I've been driving TVs for a while and "in the beginning" when there was no rules for brake lights to be turned on when regenerative breaking, I got into trouble (German highways) with cars driving behind me and not being able to anticipate / react fast enough when I used it.

I quickly learned to force the break lights and started to follow this issue closely. That's how I became aware of the number.

How the EU saddled for 1.3 and not 1.2 or 1.4 is beyond my knowledge.