Does anyone have a clear understanding of how these work/add up/stack, etc?

It appears to me that they don't stack, and in fact, go away when you get more than 1.

Ii had 1x car def +5, and 0x car def +6. I scratched off a car def +5, (which means I should have 2x now) which gave me a quest reward of car def token +6 (which means I should have 1x in inventory now). I checked inventory, and the 2x car def +5 tokens are gone and I have 1x car def +6. In my overall stats, my car defense went up 1%. So it appears that when you get two 5's.....they would go away and you get a 6, and so on???