thats right mate,
cat A is fit for 1 thing...the crusher
cat B is spares only..
Cat C and D is if the damage comes to more than 2/3 of the book price of the car then it gets classed as total loss as its uneconomical to repair (in the insurers eyes)
however claims are based on replacing all damaged parts with brand new parts, 9 times out of 10 you could probably fix the car for less than half of what insurance says damage is just by using second hand parts.
thats why so many cars get written off while having very little damage.