Does the term “The Great Bastards” apply to people like Brynden’s sisters or the children of Lord Butterwell’s three daughters (illegitimate children of nobly born women), or is it limited only to Daemon, Brynden, and Aegor? And do you think there might be other Great Bastards that we just haven’t been introduced to yet?

The term “Great Bastard” was given to all those of Aegon IV’s acknowledged bastard children from noblewomen, so it does include Brynden’s sisters, as well as Shiera Seastar. 

It doesn’t include Jeyne Lothston (who could well have been his daughter by Falena Stokeworth as well as his mistress) because she wasn’t acknowledged, or Merry Meg’s daughters because she wasn’’t highborn although those children were acknowledged, or Bellegere Otherys’ children because she wasn’t a noblewoman and there was a question as to paternity.