Now look at the second diagram, showing the position three moves into the game. Notice anything special now?
The bottom diagram, which arose from the first diagram after 1.c4 Nf6 2.g3 d6 3.Nc3 O-O, looks a lot like a King's Indian Defense (KID) in a traditional chess game (SP518 RNBQKBNR). I wanted to play 4.Nf3, preparing 5.O-O, but that leaves the Rf1 exposed to 4...Bh3. Instead I prepared the same idea with 4.Bg2, covering h3. The game is still in progress, so I can't comment on the subsequent moves, except to say that KID themes occurred on nearly all opening moves.
How many positions are in the chess960 KID family? If we freeze the four pieces on the Kingside (h-side for the purists; i.e. ****KRNB), the second Rook can be placed legally on any of the remaining squares. The dark squared Bishop has two possible squares, then the Queen has three squares and the Knight two squares (or vice versa). That makes 2x3x2, or 12 possible positions in the same family. The start position SP599 is one of the leading members of the family because the Queenside Knight can go directly to c3.
Other members of the family can be imagined by shifting the King one or two squares toward the Queenside. The twins of the KID family -- for example SP258 (BNRKNBQR), the twin of SP599 -- have a similar set of dynamics. One significant difference: in SP258, castling O-O-O is possible on the first move.