I've read reports that the 2 litre PD engines were generally less reliable than the 1.9's, partly due to the Siemens (piezo?) injectors used instead of the Bosch solenoid type in the 1.9's, however I'm not sure if all 2 litres had the Siemens injectors fitted, I'd say possibly not, because it looks like VW produced both 8 and 16 valve
TDI PD units in 2 litre form, I don't know enough about which engines were fitted to which models and from which years/ vehicle spec to elaborate any further I'm afraid but as you say, there were other issues with the 2 litre including possible oil pump failures? Scour the 'net as much as you can for info, the TDI clubs and forums usually have plenty of comment on such problems.
There was a good thread with some explanation by somebody who was obviously well versed in the problems and differences between the fuel systems, if I can find it again (never can when you want to- typical

) I'll post a link.