When were 2.0 tdi oil pump problems fixed?

For a given delivery pressure at the nozzle, the PD is no more efficient than the CR system. Both implementations by VAG use the same size of timing belt, implying similar loadings for a similar belt life.

The real beauty of the PD system is that the roller cam followers for the high pressure pump system are lubricated in engine oil and not fuel, as they are in a CR engine. This allows higher loadings and a much longer life. Regrettably, VAG made the engine valve actuating cams too narrow on these engines (Bosch got the lion's share of the cam-width space) so camshaft wear has to some extent limited the longevity of these engines - although replacement of the camshaft and 8 followers is economically feasible even on an old engine. The roller followers on a CR pump are marginally lubricated at the best of times - a dose of petrol in the tank usually kills them.

The real problem with the PD is its lack of flexibility in terms of fuel delivery timing. When the engine exhaust valves are open and (useless, wasted) fuel needs to be injected to burn out the soot filter, the PD has no pressurised fuel available. This, and the high component cost from Bosch, is the reason the PD system was dropped by VAG in favour of the CR.

The PD system is still unbeatable for efficiency and life. Look in the "high mileage" section of this site. Nearly all of the engines are PDs. 

rotodiesel.