German Five Year Stamps

Just a quick point to add GDR Five Year Plan CTOs do NOT have gum.

Since it has been several years since I placed these stamps into my album I decided to go back and do a review to ensure I had everything in the correct places. I found the 'Identification Tool For The German Democratic Republic
Five Year Plan stamps' in Stamp Smarter to be invaluable, being able to quickly filter by different variables. I did find 4 or 5 that I had placed incorrectly. I noticed the worldstampsproject webpage noted the following info regarding the CTO's:

Reprinted and reissued stamps for philatelic market were released cancelled with postmarks in black color printed directly on them. Dates on cancels were set to 1956, locations were: COTTBUS 1, DRESDEN N25, ERFURT 1, GERA 4, GERA 4, HALLE (SAALE) 2, KARL-MARX-STADT C 1, KARL-MARX-STADT 4, LEIPZIG C1, LEIPZIG O5, MAGDEBURG BPA 7, POTSDAM 1, ROSTOCK 2 and SCHWERIN (MECKL) 1.

Was wondering if anyone out there has attempted to compile full sets based on CTO cancel? The cancels cover the first 4 issues. I made a go of sorting my large pile of duplicates and started on that endeavor. Obviously nowhere near complete but I figure I can fill in holes passively as I tend to run into these stamps all the time. Who knows, in 10 or 15 years I may be close.....