Lineage is passed from man to the man who beats him. If the title is vacated for one reason or another lineage can be restored by united the three original belts (WBC, WBA and IBF). NB: Some believe it is enough to unify three of the four major belts (including WBO) and there is no consensus on this issue.
Calzaghe has little claim to being champion, plus he'll retire undefeated while Erdei will probably lose.
I thought Nate Campbell held 3 belts at lightweight. Even though one of those is the WBO, I thought this would still be enough for him to count as Lineal LW champ were it not for the fact that JMM is already. I didn't think it was vacant anyway.
Does no-one else think that there are times when fighters do actually deserve to lose their titles and no longer deserve to be cosidered champion, lineal or otherwise. e.g. Riddick Bowe when he was avoiding Lewis, or even Tarver when he took so much time off to appear in a film. Even though I've stuck up for Calzaghe on these boards, I don't really consider his Ring belt as that valid when its lineage went through Tarver, post Rocky film.