S3 Rear Diff Part Numbers ?

[MalcB]

Trying to help another member.
A couple of years ago I had the rear diff chnaged on my car. However, I bought part number OAV525010B but found the Haldex unit had to be changed over from my original assembly which had part number OAV525010K. I thought the first 3 letters OAV , OBR etc determined the Haldex unit?
Does anybody know how the part numbers are made up?

 

[ch1z64]

Check this site out and you will find . ( https://audi.7zap.com/en/rdw/audi+a3+s3+sportb+lim+qu/a3/2007-412/ ) just change the year off the model