Books 19-21 were from the Liveship Traders trilogy, by Robin Hobb. My father-in-law had lent me the first book years ago, after I finished the Farseer trilogy from the same author. I read about a chapter, excited to have another book from the same world, but put it down after that, disappointed that there did not appear to be any overlap in characters. I returned to the series after starting the Rain Wild Chronicles. It is sort of funny reading ostensibly stand-alone trilogies/series out of order. You don't need to have read the Liveship Traders trilogy to understand the Tawny Man trilogy, but there are things that remain mysteries the latter series if you haven't read the former! Likewise, I have enjoyed the Rain Wild Chronicles very much so far, but those books took some of the mystery out of the Liveship Traders trilogy.
One thing I think Hobb did an excellent job on in the Liveship Traders trilogy was keeping the characters complicated (I was going to say balanced, but that isn't quite right). I tend to dislike when characters are wholly good or wholly evil, and the character's in Hobb's other series often suffer that weakness. The characters in the Liveship Trader's are more nuanced, and I appreciated that.