There are lots of different distributors for VWs.  Most are VW or Bosch but there are a lot of other brands too.  Even within the brands, there are lots of variations.  If I'm not mistaken, the original distributor VW used was an off the shelf Bosch part that had another original application.  I can't remember for sure where I read or heard that, so I might be dreaming it up.

Some use only a mechanical spark advance (like the Bosch "009") and some use only a vacuum advance.  Some use both.  Some use a double vacuum canister that not only advances the spark, it retards it when needed.  Most have a one piece points unit, but some, like the Bosch "010" use two piece points.  There are lots of different points.  Some will work in several different distributors, some will only work in a certian one.  There are several different ways the condenser mounts too.  Even though they are all basically the same electrically, not all condensors will mount on all distributors.  Seems like some of the later fuel injected engines had some special electronics in the distributor (don't know a thing about fuel injection, so someone else will have to step in there).  The older VW distributors had the lobe for the #3 cylinder retarded about 3 degrees because that cylinder always ran hotter due to the internal oil cooler preheating the air to that side and #3 is the furtherest away from the fan.

Even the Bosch 009 has variations.  Compair a new Brazilian made Bosch 009 to a 30 year old unit made in Germany . . . they are not the same.  In other words, all VW distributors are not created equal.  There are about as many variations in the distributor as there are air-cooled VWs on the road.