There is one more important feature of these East German stamps which needs to be explained.
There are stamps which were genuinely issued for people in East Germany to use, and there were very many more stamps which were never issued for postal use. These reprints were never gummed. The cancels were printed on them when they were made. These are called "cancelled to order, or C.T.O. stamps. They were made to put into inexpensive stamp packets for collectors.
The original stamps are different printings, and they have distinguishing characteristics. The Scott catalog only briefly mentions this, and the used stamps of the original (postal) printings are not given values. No guidance is given to the collector to distinguish original printings from non-postal reprints. The Michel Deutschland-Spezial catalog describes the differences of each of the values in the set.
Here is an example of an original printing (pair of stamps on left) and a reprint. The Michel catalog describes the reprint/c.t.o. of this 12 pfennig, offset-printed stamp (on the right) as having heavy text printing.
Also, more experienced collectors can distinguish the differences between postal and printed (c.t.o.) cancels.