Why was Harry Kim never promoted to Lieutenant Junior Grade by Janeway while he was in the DQ? Couldn't she have issued a field promotion or something? I know she messed around with Tom Paris' rank a few times.
We could theorize that her promotions/demotions during their time in the DQ weren't worth the paper they were printed on, without the signed authorization in triplicate from people above her in Starfleet Command (which for obvious reasons she could not get). Ultimately the few times she kicked Paris in the butt he did always end up reverting to his original rank eventually, probably because she couldn't really
demote him. So maybe she just figured it wasn't worth the hassle trying to promote Kim, even in a semi-temporary sense, because she knew a temporary promotion might not 'stick' when they got home anyway.
And Picard made Wesley a full Ensign without him even attending the Academy.
Anything to get into Beverly's pants.
Seriously, I've always thought Wesley being given full Ensign was just plain dumb. It was the kind of thing Picard shouldn't have even had the authority to do (and if he did seek authority from his superiors for give Wes rank, then Wes shouldn't have been busted back to Cadet and sent to the academy). Sure, making Wesley an acting
Ensign is easy, that's as simple as just giving an order and then telling his mommy to sew him some special jim-jams. But an official promotion into the full chain-of-command, even a 'field' promotion, would need to be done by-the-book.