Because the Halo 4 chest piece is symmetrical,
TurboCharizard and
PlanetAlexander are correct. The unfolder was attempting to reduce the number of pages members needed to print out as those pieces are simply mirror duplicates. You really need to only print off one and then flip it over to use as the corresponding pieces on the other side of the part. It is the same reason that some Armory Entries have only a "Left" piece, like Forearm or thigh. Because those pieces are mirror duplicates you need to only print off the pieces once and then just flip them over to make the corresponding other side.