Actually....scratch my theory. I tried to cover one of the terminals on the bulb the other day and it just didn't work at all when I did it. No signal and no parking light. I'm assuming needs current continuity for the bulb to work. Each terminal isn't fed current separately.

That is correct i think....
it is like the driving light feeds 6v to the blub.
In EU they go on if you normal positioning light is out.
Why cant you in the states simply put the car in EU mode?