I think the point is that these things have not changed that much in the last four and a half billion years. Ignoring volatile stuff that has been driven off what you are left with is "primordial stuff". Even bodies like Ceres and Vesta have radically changed since their formation.
So, if you had enough stuff like this you could build a solar system. Or, at least, work out how it had evolved.
I am a body in the solar system, but you'd have a pretty hard job trying to work out how Jupiter formed by looking at my chemical constituents.