The B platform evolution was kind of weird. The 8-link style front suspension Audi A4 (Typ 8D) came out in '95 as a '96 model, replacing the Audi 80/90. The Ax naming convention had already started a year or two earlier with the Audi A6. But the A4 was the first to get the new front suspension layout (the A6 followed a few years later when the all-new C3 A6 came out).
Back then, Volkswagen was still using the Golf-based Passats... the B3 and B4. In '98, the B5 Passat came out, which was a return once again to a shared with Audi platform. The B1 Passat (sold as a Dasher here) was mechanically the same as the Audi Fox, and the B2 Passat (sold here as the Quantum) was mechanically the same as the Audi 4000. But when the B3 came out in '88, the 4000, which had gotten a couple facelifts and got renamed the 80/90, continued some platform development/improvements until the A4 replaced it.
The '98 Passat was essentially the same car as the Audi A4, and both were more or less the same underneath for 1998 through 2002, but the Passat got a major facelift mid-2001. The Audi went to a slightly different platform (to the Typ 8E from the 8D, the 8E FWD versions gaining IRS and that horrid CVT) in 2003, but the Passat carried on basically unchanged from mid-2001 to the end in 2005. They never got IRS, and they stuck with the conventional 5sp ZF automatic.
What is odd is, the AWD B5 Passat (4Motion), does not use the same rear suspension and differential as the AWD A4 quattro, but instead lifted all that from the larger Audi A6. No idea why. The C3 A6 is not drastically different than the A4 or Passat, just a wee bit larger. They actually share a lot of parts.
