The Piston remix was on the Dschinghis Khan best album, if I remember correctly
If this is going by Berryz' last release, there should also be some covers chosen by members and the most important song for each musical they did. And maybe a remix of one of their iconic song (Ginghis Khan got a "piston" version, because it didn't have enough remixes haha).
I had no idea such an album existed haha. I checked, you're right, normal version, Tartar Mix and Piston Nichizawa Two Turntable Remix are on that album.
Edit : HMV unveiled tracklist (http://www.hmv.co.jp...LECTION_7693909
「Rare tracks compilation」
1.Yuki ga CHIRARI
2.Come Together（℃-ute Ver.)
4.Kimi wa Jitensha Watashi wa Densha de Kitaku（Winter Ver.)
6.Kirai de Kirai Kirai／℃-ute
7.Chô HAPPY SONG（Single Ver.)／Berryz Kôbô×℃-ute
8.Gamusha LIFE（Acoustic Ver.）
9.Neru Ko wa °C-ute
11.Ataru mo Hakke!?
12.AKUMA de °C-ute na Seishun GRAFFITI
13.Yume (unreleased song)(new song)
14.Rin (unreleased song)(new song)
15.Zenbu Owatta Kaerimichi (unreleased song)(new song)
Yuki ga CHIRARI seems to be the original version of Sakura CHIRARI and Come Together is Ongaku Gatas' 3rd single. Neru Ko wa °C-ute is from their musical in September 2007 and Ataru mo Hakke from the one in September 2009.
But no idea about Samurai☆Baby.
3 new songs and several songs I've never heard of : I'm excited about this 6th disk.
Now hoping events will be before my arrival to Japan or I'll be tempted to buy limited A with regular.