Standard or official romanizations of non-Roman names?

Most people who currently regularly act in or direct movies whose names are in non-Roman characters have an official Roman-character name, which is often different from any standard romanization of the name in established romanization systems.

For some examples (in these, the underlined names are the family names):

斎藤 工 in modified Hepburn romanization (as specified by IMDb for romanization of Japanese) is Saitô Takumi – but the official Roman-character spelling he goes by, seen on his official site, is Takumi Saitoh (with the family name moved to last and the long vowel in it indicated by adding an h instead of a macron or circumflex). His name on IMDb is currently Takumi Saitoh (the official spelling).

濱口 竜介 in modified Hepburn is Hamaguchi Ryûsuke – the official Roman-character spelling he goes by, seen on the Japanese site and poster for Happy Hour, and the sale agent's page and poster for Drive My Car (for just a few examples), is Ryusuke Hamaguchi (with the family name moved to last and without any indication of the long vowel in the personal name). His name on IMDb is currently Ryûsuke Hamaguchi (the modified Hepburn romanization, but with the family name moved to last).

조 인성 in Revised Romanization (the current standard system for romanizing Korean) is Jo In-seong – the official Roman-character spelling he goes by, seen on his agency's site, his official Japanese fan club's site, and the Korean Film Council's site, is Zo In-sung. His name on IMDb is currently In-Sung Jo (neither the standard romanization nor the official spelling, and contravening the current rules for ordering East Asian names).

If a person's primary name on IMDb should be how their name is most frequently written in on-screen credits, then to me it follows that for a person who mostly works in Japanese-language media and whose name is most frequently written on-screen in Japanese writing, the spelling in Japanese writing should be considered the person's primary name. Because non-Roman names need to be romanized to enter them on IMDb, the name should be romanized in the standard system for the language: in this example case, modified Hepburn romanization. By this logic, the primary name on IMDb for 斎藤 工 should be Saitô Takumi.

However, the guides for both Japanese and Korean and Russian names and titles state:

Names that are already in use in English should be used as they are presented in English dictionaries and not transliterated. […] This rule should be applied mainly to composers, writers, and politicians who are well known. Other names should be presented according to the rules.

The Russian one elaborates on this with an example:

Thus, Tchaikovsky instead of the precisely transliterated Chaykovskiy.

Now, of the three examples I have given, none are composers or politicians, and none are internationally-known household names on the level of Pyotr Ilyich Tchaikovsky. But they aren't unknown, and they're maybe better known in the countries they're based in than the majority of the countries' composers, writers, and politicians.

So, ultimately, my questions to staff regarding this are: how famous does someone need to be for their primary name to be allowed to be a non-standard romanization? What are the criteria for judging this? Can actors and directors ever qualify?