[CQ-Contest] QSL from DARC

[Yuri]

Sorry for the off-topic, but maybe some of our German friends would clarify this situation for me. I usually receive hundreds of QSL from Germany through the bureau and I try to answer all of them (not in a timely fashion though).
What surprises me that every new batch of incoming cards contains up to a dozen my own cards for DL stations that are being returned with the stamp either "Does not collect cards" or "not member. Can't be delivered". But I received all the cards from the buro... What's happening?
Thanks.

Yuri VE3DZ