^ I will explain. Look at the live performances of FJ here
http://canta-per-me.net/yukis-vocalists/fictionjunction/, or search here
http://canta-per-me.net/upcoming-archives/ for "Yuki Kajiura Live" using your browser's "Find" function.
vol 1, 2, 3 werent a tour but single lives, vol#4 was the first tour, vol #5 was 2 concerts one with japanese seal, vol#6 was a 4 concerts tour with a different vocal guest on each, vol#7 was 2 concerts promoting Fiction II, vol#8 had 3 concerts, vol#9 also 3 but split in japanese seal, kajiurago/english only, and sountrack special (Eri secret guest on ost one, Hanae on the 3rd), vol#10 was a single live with a tone of guests, vol#11 was alot of concerts of FJ and 2 of Yuuka with 2 guests for Yuuka, vol#12 will again be split in japanese seal, kajiurago/english only, and sountrack special. but in a tour style and there will be day and night performances.
from all these only vol#2, 4, 9 and 11 made it into DVD, so they are releasing what they feel like witout any sort of rule.
Also they tend to release the performances with the most cliche tracklists every time and that is irritating (for example you wont see any concert without zodical sign or mezame in it - other cliche tracks are Ensei, song of storm and fire, yume no tsubasa, maybe tomorrow, sweet song) as if there arent other musics they can perform. I understand that it takes time to learn to sing the new songs but if you sell a DVD that's 45% with already performed stuff without any change to the performers that sing/play them (guests) its starting to get ridiculous.
@Hatouchan : They can also try to have a guest during a whole concert and not just 2-3 songs, like it happens in some lives where I live. If they have them for 2-3 songs, it makes no difference for the guest if there are different guests in one live, or only one, since in all cases the time they get to shine at is the MC, and the amount of songs he/she gets to sing/play, the same.