The "Classification and Rating Rules" document of the MPA outlines that anything made by an MPA member must be rated to be distributed.
"Classification and Rating Rules," The Classification and Rating Administration, filmratings.com, accessed November 30,2022
E. For purposes of these Rules, an "MPA member" is any member of the MPA, and any parent or subsidiary of such a member or of such a parent or subsidiary ("parent" and "subsidiary" relationships are those in which one legal entity has greater than a 50% ownership interest in another legal entity).
F. All motion pictures intended for exhibition in the United States produced or theatrically distributed by a member of the MPA must be submitted to CARA for rating. Such motion pictures may only be exhibited in the United States with a CARA rating and rating descriptors and are subject to these Rules, as well as the Advertising Administration Rules.
G. Any motion picture not produced or theatrically distributed by a member of the MPA may be submitted to CARA for rating in the same manner and under the same conditions as those applicable to submission of motion pictures by members of the MPA. However, the producer or distributor of such a motion picture may elect not to accept the rating and rating descriptor for that motion picture, or to surrender the rating for the motion picture, and thereafter may exhibit or distribute the motion picture in the United States without a rating.