Actually, what I meant by Cutter understanding slavery was that his people had been enslaved in Blue Mountain, and he had to get them set free. This knowledge of slavery comes within the context of the original series. And, like the earlier trolls who rebelled against the High Ones, Cutter's people had been considered lesser beings by the "High Ones" of Blue Mountain.
Cutter didn't need to be a slave himself to have felt what his tribe felt.
The other incident, in Troll Games, did occur to me-- but as Nowth said, the story had not yet been conceived at the time the series in question was written. :)
(I hadn't thought about the Picknose-Cutter incident-- but, as Innie said, that was very brief, and not really serious.)