Not really 20 years, "only" 10 ;-)
I was talking about the
Teiban series released in Japan.
After 2005 and the beginning of the -online to everything (after Nobunaga no Yabou online/internet edition, Romance of Three Kingdoms online, Uncharted Waters online and so on), there seems to be a radical shift regarding PC gaming.
There are two Nobunaga's Ambition currently sold on Steam one isn't a remake (actually the 14th one) and a remake of one previous very popular in Japan, the 6th one (I believe that this one was mainly ported to PSVita, and then Koei-Tecmo thought about Steam: "why not?"). The Romance of Three Kingdoms which will come in english is the 13th one.
Koei's prices were usually high for new games: take ¥12,800 for a strategy game, ¥13,800 if it comes with a Power Up Kit - aka a addon - or a Soundwave version - with music CD for pre-windows games. Other kind of games (adventure, RPGs or minor series) were usually ¥9,800 on PC. On consoles, when a regular console game cost ¥5,600, Koei's games were from ¥6,500 to even ¥9,800.
Think about the Matrix/Siltherine business model against the Paradox one.
The Teiban series was very interesting back then since there were windows ports (and sometimes real remasters) and for slighter price (¥1,980). But now, since there aren't produced anymore, they cost a lot more on japanese shops...