If you look at: http://anidb.info/perl-bin/animedb.pl?show=rel&aid=725 there is a loop in the relations (although it is hard to see).
Uchuu Kaizoku Captain Harlock (725) is a prequel to Harlock Saga (661) which is a prequel to Maetel Legend (1534) which is a prequel to Uchuu Koukyoushi Maetel: Ginga Tetsudou 999 Gaiden (2410) which is a prequel to Ginga Tetsudou 999 (484) is a prequel to Uchuu Kaizoku Captain Harlock (725), the starting place...
Unfortunately I don't know anything about harlock, but this is obviously wrong.
[RELATIONS] Prequel/Sequel Loop in Harlock
Moderator: AniDB
*up*
We should remove the relation between “Uchuu Kaizoku Captain Harlock” and “Ginga Tetsudou 999”, because there is already a path from the first one to the second one, via “Harlock Saga”, “Maetel Legend” and “Uchuu Koukyoushi Maetel: Ginga Tetsudou 999 Gaiden”.
When there is a three-seasons anime, we never put a direct relation between season 1 and season 3: this is the same with Captain Harlock and Ginga Tetsudou 999. The direct relation should be removed.
We should remove the relation between “Uchuu Kaizoku Captain Harlock” and “Ginga Tetsudou 999”, because there is already a path from the first one to the second one, via “Harlock Saga”, “Maetel Legend” and “Uchuu Koukyoushi Maetel: Ginga Tetsudou 999 Gaiden”.
When there is a three-seasons anime, we never put a direct relation between season 1 and season 3: this is the same with Captain Harlock and Ginga Tetsudou 999. The direct relation should be removed.