I have just finished reading "Der Zauberberg" by Thomas Mann and I couldn't help but notice that the author often leaves out the auxiliary verb (especially in the form of hatte) when writing in pluperfect. Here's an example:
Bequem und nicht ohne Würde trug er auf seinen Schultern die hohe Zivilisation, welche die herrschende Oberschicht der handelstreibenden Stadtdemokratie ihren Kindern vererbt [hatte].
I've added the [hatte] where it should be - it's not in the text. There are numerous other sentences like this that I could quote. It's just the first example I could find.
Being german myself, I can safely say that in modern Standard German it would be highly unusual if not plainly wrong to leave out the auxiliary verb like this. I couldn't find any rules about when it's allowed to be left out.
So what is going on? Is it just an old grammar rule that I am not used to, or maybe just writing style?