These sources are all saying the same thing, you just have to know how to interpret their different notations. Orberg is giving you the 2nd and 3rd principal parts, so it’s reviso, revisere, revisi. 501 Latin Verbs is not saying that all the principal parts are formed like duco; they just mean that it’s 3rd conjugation, and at least the first two principal parts will be like duco. I would guess that reviso is rarely used in the perfect passive (due to its meaning), so the 4th principal part might not exist.