I don't think you're seeing it quite right, and I can see why.
Where the number of current-carrying conductors in a raceway or cable exceeds three,...
1st scenario: A conduit or a cable, with more than three CCC's in it.
...or where single conductors or multiconductor cables are stacked or bundled longer than 600 mm (24 in.) without maintaining spacing and are not installed in raceways,...
Second scenario: groups of cables or conduits. I think their point was, there does not have to be a raceway containing the cables to consider them bundled.
I think it would more clearly state their point if it read "(24 in.) without maintaining spacing even when not installed in raceways," IMO.
Also see note 4 to Chapter 9. It reiterates that a nipple less than 24" does not require derating, which seems to infer that over 24" it does.