as ive said a few times i dont think that lightsabre every belonged to anakin
ok heres my theory
obi wan knew that luke was anakins son and in knowing that the force would be strong in luke. He told him it was his farthers and he wanted him to have it
so that luke would want to be a jedi like his dad
i dont know it could be a spare one or something or one he found whatever
but i dont think it ever belonged to anakin in the first place
what gets me is that if obi wan took luke away from his mother and left him with owen and beru why he didnt try to train him as a child or even take him to dagobah or had him and yoda just given up