They try to follow the original parts numbers as it avoid confucion. So do Rimmers.
I used to use Paddocks a lot but the last few times I got the YTS and I end up having to explain stuff to them, even then I don't get what I asked for.
I find rimmer's not the cheapest (he said politely) but if they say it's in the post it's in the post, handy if you are VOR.
Anything I'm struggling with I follow the advice of others and ring Devon 4x4 now.