I noticed this last night. In the Atlas version of Blood of the Valiant. The information on Sun Chen is missing. No stat block or decption text. Glimpse of the Abyss, however has a refrence to Sun Chen in the adventure in it. The page refrence Glimpse gives is to the Ronin edition.
I was thinking of sending Atlas an email asking if they could post the missing text . I have the Ronin edition, by the way too. So I could post the text if that isn't a problem.