The 1998 Erler catalogue update lists several congress style sets from the 1940s and 50s. I do not know if they are FDGB issued.
Budapest Conference 1959, written in English
IG Bau-Holz (Carpenters Trade Union) 50pf black 1949/1950?
Kreis Sonneberg (Sonneberg district) 1945 FDGB control marken?
Admission ticket 100 marks
Marked Vietnam fund, any explanation welcome.
GKB stamps found alongside FDGB stamps in an early booklet
A strange booklet as Kassel was in West Germany and with fgdh? and IG Metall stamps
Allotment Assistance National Committee of Saxony
Garden help beitragsmarken with FDGB in red
Social Insurance stamps
The IG Wismut union sometimes used a green 6 vertical lines overprint on Beitragsmarken starting with the D10 in November 1949.
In 1953 it changed to 3 horizontal lines and in 1955 the overprint changed to one horizontal line in green and then one line in black with the D21 issue in 1957.
I have not seen them used later than on the D22 issued January 1960.
So far I have about 50 differant, I have not catalogued them but suggest a "w" prefix to the oringinal cat number.
West Berlin overprints
A "W" or "DM" overprint hand stamped or printed on Beitragsmarken and Spendenmarken Signifies that the member worked in West Berlin, The probable reason for this would be as a train operator this was due to the designation of the East German Deutsche Reichsbahn in post-war treaties and military protocols as the railway operator in West Berlin. Therefore these overprints are rare.
Hand Stamped Overprints
Control numbers are usually found in the bottom right-hand corner of the sheet, They are almost always torn off so that the stamps can fit in the book
Due to the poor printing standards stamps are regularly badly centred, for this reason although not ideal I do not consider poor centring to be a fault, Surprisingly extreme examples like the May Day 1970 are not common.
I think these are a D1011 80pf brown and D1002 10pf brown missing the value and 1950 overprint.
I have come across this a few times but can not see it being anything but an error.
A A2901 with extreme yellow and orange colour shift