lol. The VAG group has internal model names for each car. These typically take the form of a three letter code like 8L0 or 8D5 or 1J0.
There are also names for the general platform the car is built on. These names originally started out using a letter and a number, where the letter signified the platform type, and the number the generation. The letters are A/B/C depending on the size of the car. In more recent years this has changed a bit however.
So for instance the A1 platform is a Mk1 golf. A3 platform includes Mk3 Golf/Jetta. A4 platform covers a wide range of cars, such as the Mk4 Golf, A3, Leon, Beetle, Toledo and Octavia. Each of these also has a model number, the mk4 golf is 1J0, A3 is 8L0 etc.
Its just odd that everyone uses the platform to describe the A4 and A6 ranges, they'll say B5 A4 or C5 A6 rather than 8D0 or 4D0.