https://musicbrainz.org/doc/Style/Miscellaneous says roman numerals should not be used, but it's normal for roman numeral characters to be used in Japanese. It's also inconsistent to not apply the standard of "Use of basic ASCII punctuation characters such as ' and " is allowed, but typographically-correct punctuation (such as ’ for the English apostrophe) is preferred" to roman numerals. Same as hyphen vs. minus or apostrophe vs. prime, roman numeral (singular) vs. multiple ambiguous ASCII characters affects machine sorting and tokenization.