I'm of the opinion that someone who interprets the requirement in such a manner is going to do so regardless of the redundancy. The requirement as it is written currently can be interpretted to allow multiple nipples of 24" or less because it uses the plural of nipple. It does not limit a single raceway length to 24".Smart$,
If they didn't use both terms, then what would stop someone from using 2 or 3 24"
nipples coupled together ? Just a thought.
Perhaps it would be better stated something like...
(4) Where the total length of a conduit or tubing raceway between boxes, cabinets, and similar enclosures does not exceed 600 mm (24 in.), the raceway shall be permitted to be filled to 60 percent of its cross-sectional area, and conductors therein shall be permitted to be exempt from 310.15(B)(2)(a) adjustment factors.