VE (short for the German word 'verteiler', which is 'distributor') is what the early TDIs used, which is an older type diesel injection system that Volkswagen started using way back in 1977 when their diesels came out. The TDIs used an electronic controlled version of the Bosch VE pump. Then came PD ('pumpe duse', which is 'pump injector') that uses individual electronic controlled mechanically activated (off the engine camshaft) injectors one per cylinder. Then finally, and sadly, lastly, came CR, which is common rail (which is the same in German) that uses a pre-pressurized fuel chamber, or "rail" which is a long cylinder that is fed fuel via a high pressure fuel pump that supplies the totally electronic controlled injectors (either by piezo-electric wafer stacks or older design solenoids that have been tweaked) to provide the even higher pressure but super precise fuel metering into the engine.
The CR is superior in every way, in that unlike both the VE and PD, it is not constrained by engine mechanical position for timing control of the injection event. It can be done completely independent of any mechanical timing of the engine. So things like staged pre-injection, post injection (for exhaust emission control equipment function) as well as an infinite range of both timing and quantity can be easily handled. That is why they can start so easily, run so quiet (relative to older diesels... although the VAG and especially MB CR diesels at hot idle are barely any different that their modern DI gas counterparts), and get such great fuel economy (potentially). But the emissions compliance strangled and ultimately removed them from our availability. You can still buy as many 12 MPG Suburbans as you like, though, the EPA has no problems with those.