joveian: The other oddity about the way this was done is that the "a game you have been waiting for is now available" email was just sent now, not when the extras were available. It isn't a DLC, just a partial artbook and partial soundtrack. Nothing that affects the game (pre-Falcom's "unreanable number of pointless DLC" era I guess) and nothing worth worrying about not getting IMO.
The partial soundtrack is 10 tracks, great if you like those songs, although the soundtrack as used in the game is available in opus format in the game_pc/bgm directory (without metadata, though). Falcom sells CDs of the full soundtrack (look for the soundtracks on
this page, the evolution one is 80 tracks and this version is based on the Kai version which is a remastered evolution version).
I took a quick scroll through the partial artbook (quick due to spoiler warnings) and it has a map, main character portraits with a bit of text, and a few pages of screenshots. A total of 19 pages. Falcom likely had a much longer artbook available at one point, although it isn't showing on their web site and the text would be entirely in Japanese.
Cavalary: didn't keep copies
joveian: Luckily, the very archive page you linked to saved a copy :).
You can also buy the MP3 version of the Zero OST on Amazon (Amazon music is DRM free btw)