I'm not an expert in the legality of things concerning this distinction. I'm not saying that he should automatically get money for all his claimed contributions. But if he contributed bass lines for songs that got released (i.e. HT20) then it should be natural that he receives money for it IMO. As I understand it he should have writing credits for some of those songs (e.g. "Could Have Been") and therefore should be eligible for royalties from them. It needs to be clear what he contributed where and whether he in fact got "erased" from tracks he performed on (e.g. HTEP). Time will tell.
It seems a bit far-fetched to me, though, that he "will come back for more" because he can't claim anything more than what he in fact contributed (if so, of course). Why it took him 20+ years for this, I don't know. Still it needs to be evaluated.