Classification is based on the cars value vs repair costs not damage.
For example
10k car with 8.5k damage will be D
Same car with amended estimate to 8k will be repaired and not recorded.
£600 corsa with a very light scrape £600 repair will be C
Nothing is clear cut with write-offs and the whole process is bollocks. Just repaired a Merc E class with 19k of damage which will go back onto the road and no one is any wiser.