Whats the letter for after Audi part number?

[A4B6Cab]

I have a cab and a lot of parts for it the number is the same, but the letter is different at the end, is this significant? Just wondering in general, but am after front fog light units and the long number is the same for the cab/saloon/avant, but the last letter is different?

Would be good to know anyway

[zollaf]

it normally signifies a revision to the parts design. sometimes its a just a little change, sometimes a bigger one. some will interchange, some won't.

[Crasher]

Pretty much as Zolly says but sometimes I think they just do it for fun, they even change the initial model prefix (e.g. 8E) to the later cars prefix (e.g. 8K) and bugger all has been done to the part but then they may change just the end letter and it fits completely different brand of car! God help you if you get into the regime of central connivance [sic] units which have a colour code after the letter! I mean, why would the central locking unit have a colour code even when the only difference between two units is the soft coding it comes with.....