Pelikan introduced M481 in 1983. The model was an economy model of M400. In 1985, M200 wit a steel nib was introduced, replacing M481. In the same year, M250 was introduced. The model  had the same shape as M200, except for the nib. M250 basically had a monochrome 14 carat gold nib. It was probably introduced as a model to fill the gap between M400 and M200.

Interestingly, in Japan, the model was offered with a monochrome 12 carat gold nib under the designation #250 (see "The Pen 1986" (Japan Import Writing Instruments Catalog)(万年筆評価の部屋))⁽¹⁾. Also only in Japan, model #350 with a bicolor 12 carat gold nib was introduced around 1989 (see Japanese Pelikan catalog 1989 and 1990 (Pelikan’s Perch)). According to "The Pen 1993" (Japan Import Writing Instruments Catalog), the price of #350 with a bicolor 12 carat gold nib was ¥21,000, while #250 with a monochrome 12 carat gold nib was ¥20,000. The difference between a bicolor and a monochrome nib was only  ¥1,000. By the way, #500 (Japanese designation of M400) was ¥30,000. Around 1995, #350 was recovered from the storefront (in Japanese Pelikan catalog 1995, #350 was listed no more, only #250 was listed (万年筆評価の部屋)). Apparently, the company reorganized and consolidated its lineup to eliminate inconsistencies in its pricing policy (万年筆評価の部屋). Also, the monochrome 12 carat gold nib was probably discontinued by 1997 and unified with the monochrome 14 carat gold nib. One theory as to why 12 carat gold nib was discontinued is that the durability of nibs might have been a problem. In general, the lower the gold percentage in the nib, the stronger the nib, and thus the more pressure it can withstand. In 12 carat gold nib, the letter "H" was placed in front of the nib size (e.g. HF, HEF). Interestingly,"Hxx" nibs were not necessarily hard (Pen Cluster)⁽²⁾. "H" might have meant "capable of withstanding hard use" ​(Pen Cluster). There must have been a demand in Japan for nibs that were are resistant to high writing pressure and strong flexure. On the other hand, the nibs were very susceptible to corrosion, so it was necessary to keep the nibs clean at all times. Kubo Kogyosho: Japanese fountain pen manufacturer and repairer (probably repairing Pelikan fountain pens at the request of Pelikan Japan) had a mountain of cracked 12 carat gold nibs that were discarded when they were replaced ​(Pen Cluster).

In 1997, the specifications were changed: a ring was added to the turning knob and in turn the cap tube had a single ring. The Pelikan logo before 1997 had two chicks and was engraved, after 1997 the logo was embedded. Another specification change was made in 2003: there is only one chick left in the nest and nib (Pelikan-collectibles.com). M250 was discontinued in the late 2000s (the last catalog reference appears to be the Pelikan catalog (2006)).

Note;⁽¹⁾The Japanese Pelikan catalog used "#" instead of "M".
⁽²⁾My 12C HEF nib is also not harder than my 14C nib.