I think there's a big misconception with the term "written off".
It's a term for a body not wanting to persue the recovery of an object.
Simplest explanation which I thought of earlier. If you drop a crisp in dog s**t, you write it off, it's not worth picking back and dusting off, a little extreme I know but hey there's a reason.
On the other hand, I could drop a crisp on my kitchen floor, IMO perfectly fine to eat, but if I just couldn't see the sense in bending down to pick it up, I'd leave it again although it's a very minor problem (me not being bothered).
Insurers writing off a car from their agreements with the policy holders is along the same lines.
In one case, it could be a super rare car, and the insurers want nothing to do with paying for the replacement parts that will have to be custom made or sourced from Quebec.
On the other hand, it could actually be a real case in that the car will never be the same again (like the crisp in dog s**t), and that they'll write it off because it's simply irredeemable.
Cat X is what your car will have on record if you've ever claimed for a prang. It could be as minor as a new bumper.
Cat F is for cars damaged by fire, (off topic.. I once heard there was a V6 on fire, anyone else heard that??)
Cat D is just the insurers not wanting to bother with a possibly costly repair compared to simply giving you a book (under) valued amount for the loss of property, I would say more often than not, the customer takes that figure although I do not recommend it to anyone.
Cat C is when there is the car will cost a lot more to repair (at main dealer parts and labour rates) bringing it back to roadworthy status. The car WILL need a VIC test before it's legal to join the road network again.
Cat B is serious damage, spare parts may be taken from the vehicle before it is inevitably crushed.
Cat A is.... Well as bad as a crash can get, the police will have it crushed, and no parts may be taken from it.
IMO OF COURSE!!