In addition to JanetM's comment, your confusion may be coming from one of the cautions in the Form 5500 instructions. This caution refers to the fact that Puerto Rico plans should only use Code 3C when there is no election made under section 1022(i)(2). If an election was made for a Puerto Rico plan then Code 3C does not apply.
This caution does not, however, preclude Code 3C from applying to other types of plans besdies a Puerto Rico plan.