The Pecards does indeed work on the distressed lamb in that it darkens it down a little, from what Ive seen. I don't own a jacket in that skin but check out Major West`s posts on this thread. He owns a ToD in distressed lamb, I think, and that's a beauty, if a little pale in colour.
It works on the standard lambskin too, in that it will help water proof and protect the leather, doesn't really darken it though.
As for the difference between the two, Ive found the standard lambskin to be fairly lightweight, depending on Westeds current batch, and very soft with quite a distinct shine when new, and an even colour. The pre distressed cow has a slightly paler colour, is heavier (which helps it drape beautifully in it opinion) and has a generally more rugged look. Ages really well and breaks-in fairly quickly. Again, there are some great examples of these skins on this thread.