In English Round 1 (C) states “One piece composed after 1990” but the Japanese version does not specify as one piece. I am wondering which is correct.

A3:
We are sorry for the confusion. The Application Guideline is prepared in Japanese, English, and French. If there is any inconsistency or conflict between them, the Japanese version will always prevail.
Therefore, the English version should be “one or multiple pieces composed in and after 1900” (p. 18) and the French “Une ou plusieurs pièces composées à partir de 1900” (p. 30).