The IMDb is a database of productions from around the world since the beginning of filmed entertainment, indexing credits for a wide array of professions. SAG is an American labor union for actors and its rules only apply to credits for actors in productions made under contract with the union.
It would be patently unfair for us to try to apply their rules to other professions, productions that did not have a contract with SAG, actors working in other countries, or in films produced before SAG even existed. It's therefore not uncommon to see different, unrelated people sharing the same name.
To avoid confusion between two or more people using the same name we
usually add roman numerals to their names.