The 2 pieces of serienscheine notgeld above, issued in Hamburg, show one such example of an 'error' note. The black circle on the 1st note has a '1 mark' in it and is the normal note. The 2nd one, has nothing in the black circle! This obviously makes the 2nd note more desirable to collectors . Several variants of a note may exist, including colour differences and such things as pieces with printers names on and similar pieces without a printers name. Some notes have account numbers (konto numbers) on them as usual, so one that does not, could be listed as one of these 'error' notes, in my opinion. Several collectors would pay hugely differing amounts for these 'error' notes. Keep an eye out on the notgeld you buy and see if you have anything unusual.