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, the models 20 and MK20 were revised in 1969 (the model MK20 was discontinued in the same year). Between 1970 and 1971, the model MK10 and the luxury models (M30, M60, and M100) were revised (Pelikan-collectibles.com) (or 1971 (Pelikan Schreibgeräte)), and the luxury models were equipped with 18 carat gold nib. The model M21 was also introduced in 1971. 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. The model M480 was the longest running of M series and was discontinued in 1983. As stated above, the M series was produced for a long time, from 1965 to 1983, but failed to become a mainstream of Pelikan fountain pen or produce a hit like the model 400. It was with the reintroduction of the model 400 that Pelikan finally managed 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 ).