I agree that your example does not require that you retain the boldface -- but to answer your question:
The code does not cover the situation you questioned. You cannot use the bold face indicator for letters which applies only to the letter which immediately follows it. You don't individually bold face the I and V because they are not individual letters. That leaves you with the open and close bold face indicators which could cause a problem with the hyphen that follows. If it were absolutely necessary to retain a distinctive typeface in your situation, I think another method would have to be developed -- either a tn stating that the roman numerals are in bold face, or perhaps enclosing the bold face roman numerals in grouping signs not otherwise used in your text.