Wilbuz,
I don't know how German preasurized cockpits worked, but in the Spitfires that were preasurized (none of the ones we have in AH) the preasurization was not what we think of nowadays when we talk about presuriztion. It was better than not, but essentially kept the cockpit preasure as though the aircraft were 10,000ft lower or so (I don't recall the actually number).