I believe Lessers and Butters are the same gene, RDR has even produced a Platinum(a butter daddy similar to the original platty daddy) from a Butter x hidden gene carrier(original lesser sib). It seems clear they are just different lines of the same gene much like the different lines of pastels.

Mojaves appear to have the same gene that causes leucism in the super form and white sides in one gene carriers. I think they just have other genes influencing pattern. I bet if you bred mojaves repeatedly to reduced pattern light colored normals, you could make something that looks like a lesser/butter. We've already seen pics posted here of light colored mojaves that have been confused with lessers.