In Author, Author, Kim's mother asks why he hasn't been promoted, he hastily says there aren't many positions to be promoted to. She then threatens to speak to Janeway. Part of the humor is supposed to be that Mama Kim doesn't understand and the rest is supposed to be that she's going to baby Baby Kim anyhow. I'd say this was an official explanation.
Another way to put it is to say that Tuvok was plainly promoted in order to put him third in line. Paris was not strictly speaking promoted. The only sense in which Kim was passed over is in suggesting he could have been promoted over Paris, after Paris was demoted. But, the Kim character was introduced as a sidekick to Paris, so that wasn't going to happen. Also, speaking as an adult, a Wang promoted over a McNiell?
What I've never quite got from these recurring threads is why anyone actually thinks about Kim's promotions or lack of them? Most people like Paris and dislike Kim, which pretty much explains why the writers didn't care to write much for the character, including character promotion.
The pleasure in playing a woman in period costume begins with the underthings.
Velcro has no place in the build up to an authentic historical experience.
How do you know this?