Masashi Kishimoto is credited as the "creator/supervisor" from chapters 1 to 80. Ukyo Kodachi is credited with "script" from chapters 1 to 51 and publically stepped away there. The anime stopped crediting him as "story supervisor" with ep 217 as 216 was the last to adapt a chapter by him, namely chapter 51 (I trust Wikia as I only follow the manga). He literally said on Twitter that he will now simply enjoy the manga as a fan when his leaving was announced.
Mikio Ikemoto was always only the artist and didn´t even do the NAME (rough storyboards) when Kodachi was on story duty to my knowledge. I am sure that Ikemoto has the freedom to change things but he is simply there to execute someone else's vision in the form of art or the credits would be different, at least after chapter 51.

So who did chapters 52-80? Kishimoto would be credited differently if he fully plotted this thing. I can guess all day long but there has to be some info out there. Even if I failed to find it. Nearly 300 eps of anime are based on this, occasionally.

I also read EU/US comics and am a librarian.
Manga-Masters, My ANN-Lists + Imdb

The question kind of confuses me but I looked at Vol. 14's Japanese cover, which Wikipedia says is the first one that reverted back to Kishimoto and where Ch. 52 starts, to see the credits: https://m.media-amazon.com/images/I/919knzpGW6S.jpg

Kishimoto is credited as 原作・監修 - if you go to Wikitonary, you can see these are defined as 'the original work (such as the source of an adaptation or translation)' and 'editorial supervision,' respectively. However, 原作 is used when there is a separate artist and writer/story-creator.

You can see it here for Death Note (vol. 1): https://m.media-amazon.com/images/I/71yshzgt0FL.jpg
And again here, for Bungo Stray Dogs (vol. 1): https://i.ebayimg.com/images/g/ksIAAOSwpEtj6heE/s-l1600.jpg

There are other examples, too. Personally, I think his name is slapped on there and he's really just collecting a paycheck while ghost writers crank out chapters -- but as far as the straightforward question, it's supposedly him. I did some digging and found that on Vol. 1 of Boruto, Kodachi is credited as 脚本 or the scriptwriter. This isn't a credit I am familiar with so I am curious on what Kishimoto's involvement was from ch. 1-80 (plotting? while the other guy executes the scripts and actions to get from A to B? - this is the definition I found of the manga scriptwriter: "The manga scriptwriter will explain how many grids there are on each page, what kind of scenes are in each grid, what perspective to choose, and what dialogues or explanatory texts are there." So definitely feels like the primary, hands-on writer).

Either way, I don't see why Kishimoto's credit would change considering he has always been credited for the story in the manner that is appropriate for him as the "original" author, but I am confused about the arrangement as a whole & by the remaining 監修 in his credit. Again, my theory is that he's kinda cashed out of this franchise; even if he's still making calls in some way, I think there's a whole team around this that makes his life a lot easier.

http://i.imgur.com/LxhWm.jpg (will reformat this some day…)

Kishimoto is credited as "creator/supervisor" (in English) on Vol 1-18 on the official German release. Ukyo Kodachi is credited with "script" on Vol 1-14 and then disappears. Yes Vol 14, despite Vol 13 closing with his last publically credited chapter. Mikio Ikemoto is credited for "manga" on all covers. Amazing.

The French Covers have the same credits as the US ones described in the OP. I am VERY curious how the credits will be on the return from the hiatus chapter that leases in 7 days. A time skip looks likely so a story reset has to have happened even if the manga always leads up to it from page one. The big takeaway here is that Viz´s print run and Mangaplus credit in the same way.

Bonus round: Dragon Ball Super has its own canon and who is writing this issue but far less extreme. Toriyama is credited for "concept & story" to this day, even after the manga overtook the anime so Toriyama is taking credit for the 2 manga original arcs set before film 3 Broly. Toriyama further on record that Toriyama was involved there. No drama here, just canon confusion and off screening of 2 out of 4 films. Both the manga and anime adapt from a Toriyama outline, or so the story goes. All 4 films are further fully scripted by him. We also know that Toriyama has given input on the manga´s art and critiqued compositions and unclear layouts according to Toyotarou. To make this short. Toyotarou manga (released in V Jump from the start unlike Boruto) is his interpretation that includes dialogue and full-on layouts. No drama will start if such a question is asked on a DB forum outside of the one true canon side issue. But asks who is doing Boruto anywhere and watch the drama unfold...
The manga arcs in the Boruto anime also seem to be a bit different than in the manga but nothing crazy different to my knowledge.

Edit: Neither the US release nor the Japanese release of Chapter 1 of Part 2 changed up the credits. The mystery goes on.

I also read EU/US comics and am a librarian.
Manga-Masters, My ANN-Lists + Imdb

Naruto fans are passionate, I guess. :^) I always err to the side of what it says on the Japanese cover since subtlety can get lost in translation.

I think, although as you say it's not clear, that Kishimoto could be doing something similar to Toriyama...except for the ghostwriters don't get their dues. Ukyo Kodachi was an established writer before this and had worked on the films as well, so it would be remiss to not credit him fully, but maybe the team he has now are still "paying their dues." It's probably a steady paycheck anyway, even without direct credit. So, sort of a writer's room and Kishimoto is the show-runner, maybe?

I don't think it's anything that needs to be drama -- he doesn't even draw the series anymore (and I really liked his art-style, no disrespect to Mikio Ikemoto though) and he's been working on Naruto for over 20 yrs at this point. I'd want to just relax if I was him, too. Lol.

http://i.imgur.com/LxhWm.jpg (will reformat this some day…)