is more on company copyrights...
like you cant say this song is her best song, where is a duet song which also belongs to other singer...
that why i dont include singles that include other artist
(you know nana dont only make single with TM.R you know? this not her 1st time it just amaze that king and queen anisong singing together >.>;; lol)
then also songs is make by another artist, she wont put it in her single, mostly will be in normal album in her own ver. (e.g. Egao no Yukue is original belongs to Japanese pop band, Dreams Come True)
singles is solo original belongs to her, where all their bloody sweat hard work put inside XP...of course normal album they do unless they planning to put cover songs inside lol
but Best Album will be more of less work since is just putting your best songs inside
(for nana case is only singles' A-side + some best B-side + anime chara songs + 1 new song)
^this why i not looking forward to museum ^^;; only 1 new song XP