Interesting 1948 German Advertising Overprint On Pair

Hi I purchased this interesting Soviet Zone stamp which is one of a joined pair. The second stamp has been obliterated by advertising. I did not see a thread on these.

Has anyone seen this one and is there a reference? Are there others? This is not a cinderella to be added onto an envelope to advertise. This is a real stamp in a pair that is obliterated to advertise.

I look forward to any information anyone can provide.

Hi I did a quick re-search and found the following details which may be relevant and helpful. From a German seller with a similar pair for sale.

946a Zd overprint "2. Nordd. Briefm.-Handelertag 1948"

Brand pair from a chessboard-like overprinted stamp sheet as described in the Michel special. This overprint was specially made for the "2nd North German Postage Stamp
Dealers' Day 1948 in Flensburg" and represents the famous Flensburg monument "Das Nordertor". Pair of stamps...

This is noted and illustrated in the Michel catalog, described in brief as a "private zusammendrucke".

There is an earlier one also listed and illustrated in Michel:

(not my stamp)
Described and illustrated by Michel as a private overprint. The printed part alternates in rows with a 1937 Stamp Day design, checkerboard-style. Both yours and this one are unpriced in my old catalog but are seen often enough.
http://www.pvoller.net/new_stamps/germany/1937.php

Not sure if any other contemporary/valid stamps were privately overprinted in Germany.

Nice! I've not seen either of these overprints before.

The first one was overprinted on a stamp issued for use in the combined British, American and Russian zones.

Flensburg was in the British zone.

The Nordertor gate is impressive:

Great replies thank you. I do see online a block that shows how these were printed on sheets. Must have been quite an enterprise. I will see if I can load up the picture. Thanks also for the picture of the gate. I love items that have a story behind them.