Was there any other post-production CGI work done?

CGI touch ups are part of the post-production process so most likely

I mean since it was officially "done" in November..

I mean, if you got the time to make it look better, you make it look better

Time is money though--The longer they spend on post-production, the more money the production is siphoning.

I think it's probable some of the early trailers were cut before picture lock, but merely released after the fact. We don't know the timetable in which the trailers and TV spots were finished.

That being said, I personally don't notice any enhancements.

G. H. (Gman): That doesn't mean it never happens in Hollywood. 

As for enhancements, I don't know. Ghidorah does look noticeably better in the latest teaser. Maybe the earlier trailers just didn't show that much, but the details of Ghidorah is more apparent.

Yeah, there ARE enhancements.

Many shots look sharper or are given additional detail, such as the scene of Godzilla's call-to-arms. Many have highlighted how Godzilla's features are more detailed, and his eyes are glowing during the scene compared to the original SDCC trailer.

We see more examples of these throughout the trailers, though it can be hard to catch if you're not experienced in analyzing CGI.

Godzillatheking123,
No, you're right. It absolutely does happen in Hollywood. But the difference is Godzilla: King of the Monsters has already had one of the longest post-production periods I can remember in recent blockbuster history. Even the Russo Brothers confirmed people didn't start working on the bulk of Avengers: Endgame's post-special effects work until 5 months before its release (November, 2018). While principle photography wrapped in January, additional filming took place later with a larger re-shoot period than most films in September, 2018.

Godzilla: King of the Monsters on the other hand, was confirmed to have wrapped filming in September 2017 and was officially in post-production for 14 months. (Barring an unconfirmed week long re-shoot period in March, 2018.)

It's always possible they brought it back for touch ups, I just have a hard time believing it stayed in post-production for that long--The longer it's in post, the more money it siphons from the studio. And the more it costs, the more it will inevitably need to make at the box office. So keeping a movie in post for too long begins to work against it.

Which is why I feel, if there are differences, it's simply because the early trailers were cut before picture lock.

G. H. (Gman): "Which is why I feel, if there are differences, it's simply because the early trailers were cut before picture lock."

Yeah, that would make sense.