[vbat99]

OK, so how Kodi works is when set for scraping with Local Information Only scraper.
First Kodi will check if there is a local nfo.
Then checks for local artwork, actors, trailers.
If the artwork is not local, then - and only then - will it use the url in the nfo to download the artwork from the internet.
the same goes for Trailers. If Kodi finds a local trailer file, it Almost Famous (2000)-trailer.mp4, Kodi will use this path for the trailer first.

The urls in the nfo are only like a second-option for Kodi if the media is not located with the video file.

So, in my case where I have my actor thumbs saved in a central location (thanks to MC), I need to make sure that those URLs are accurate in my NFO file, correct?
Example:

    <actor>
        <id>0041089</id>
        <name>Martin Starr</name>
        <role>Todd</role>
        <thumb>nfs://192.168.2.5/data/stuff/misc/KODI/art/thumbs/M/Martin_Starr_0041089.jpg</thumb>
        <order>2</order>
    </actor>

A problem that I am running into is that MC and another program (Ember) have very different ideas on how to format a NFO, so when I try to use Ember to fill in what MC is missing, I lose my nice 'local-only' setup.
I wish one of these programs would allow updating only a certain section of the NFO... I know, wishful thinking that two entirely seperate programs would write code to account for one another...

Yep, so the actors thumb url is now nfs://192.168.2.5/data/stuff/misc/KODI/art/thumbs/M/Martin_Starr_0041089.jpg and not a http url.

What data is missing form MC that requires Ember?
Unfortunately, without knowing what Ember sets, or what the data is for, MC just loads the nfo and any tag not known about gets discarded. Then on Write nfo, MC writes the data we know about.