In the late 1968, school pen Pelikano was revised again (from model 2 to model 3). The model was characterized by flat and angled nib and new thermic-regulator. Accordingly, the adult piston filler pens were revised similarly with a new nib and a new thermic-regulator between 1969 and 1970 (Pelikan-collectibles) (Please also refer to P28). For a start, M20 and MK20 were revised. Between 1970 and 1971, MK10 and luxury models (M30, M60, and M100) were revised, and M21 was introduced. From August 1970 (Pelikan-collectibles.com) (or 1971 (Pelikan Schreibgeräte)), M30, M60, and M100 were equipped with 18 carat gold nib. Around 1971, the structure of the thermic regulator was changed. Starting in 1973, model numbers were converted from two digits to three digits⁽¹⁾. This led to the reduction of the M series lineup to M480 and M60 for the domestic market (Pelikan catalog No.250W (1977))⁽²⁾. It probably had something to do with the fact that Pelikan was focusing on cartridge fountain pens at that time (Pelikan - ein unternehmen schreibt geschichte), and that the piston filler models 400NN and 120 were reissued in 1973. M480 was the longest running of M series and was discontinued in 1983. M series was produced for a long time, from 1965 to 1983, but failed to become a mainstream Pelikan fountain pen or produce a hit like model 400. With the reintroduction of model 400, Pelikan was finally able to regain its former greatness in the fountain pen business (Pelikan: Ein Unternehmen schreibt Geschichte).

Note:⁽¹⁾I don't know why, but M60 and M100 were not renamed. 
⁽²⁾M100 continued to be sold in foreign markets such as Japan at least until 1980 (万年筆評価の部屋 ).