The "Castles and Palaces" small definitive series of stamps of West Germany and Berlin were issued between 1977 and 1987. All of the values were printed in one color by traditional typography. Most of the values were undoubtedly reprinted a number of times because of massive use.
In 1987, near the end of their use, some of these stamps were reprinted by a different method which Michel calls "Indirekter Hochdruck (Letterset)" or indirect high pressure (letterset). This printing method produces a much sharper and smoother print than the traditional typography as used on the older stamps.
The West German values printed by "Letterset" are 10 pf., 30 pf., 50 pf. (green), 60 pf. (dk. red), 80 pf. and 300 pf.. For Berlin, only the 10 pf. and 30 pf. stamps were so printed.
The letterset-printed stamps were undoubtedly printed in much smaller numbers, and some can be tough to find. They cannot be distinguished from the older printings by the naked eye, but 10x magnification makes identification routine. The overall printing and corners of the frames of the letterset-printed stamps are very sharp, and the print color appears even/smooth, as shown below in the close-up pic.