Sounds like someone got a nice Christmas present this year!
Getting music artwork to show up right is a real bear. I struggled with this quite a bit when I had my last two cars with this system.
The crux of the problem is the aforementioned Gracenote database. There has never been an official update, though newer cars came out with newer databases preinstalled. If you've got a 2014, it's likely got the latest version that was released. It is highly unlikely that it will ever be updated, so you'll be stuck with no artwork for anything new that comes out.
In order to fully understand how to get the artwork to show up, it helps to know what Gracenote was supposed to do in the first place - which is NOT what it is being used for in these radios. Gracenote was originally made back in the day to help out with ripping CDs, and also for displaying the artwork on the fancy CD players with color screens. You would simply insert the disk, and the onboard database would identify the CD and automatically show the artwork and provide information for tagging the resulting MP3 files if you wanted to rip them. It wasn't really made to actually identify the MP3's themselves. I'm sure that the radio would work flawlessly if you used a retail CD, but in the entire time that I owned the cars with this system, I never put a real CD into them - and I'm pretty sure I'm not the only one...
In order to get the artwork to show up on the 8.4 screen, the tags need to be correct, at least as far as what the radio is expecting to see. This does not necessarily mean that the tags are wrong for missing artwork, rather they're not what the radio needs to make them display correctly. It's fixable, but it's not easy to do - and sometimes the tagging needs to be "wrong" to make the pictures show up.
I was able to get around 95% of my music to show up, but due to the pain-in-the-butt tagging requirements, I ended up using a 2nd music library that went onto an iPod Classic that lived in the car. For every other device that I have for music, I used the normal, correct-for-everything-else tagging.
Part of the problem is due to the way that I (and I'm assuming a lot of other folks) get music. It's been a very long time since I ripped CDs to get MP3 files, so most of my music is downloaded. This means that a lot of the less-used tags aren't present. Most of my music only had tags for Artist, Album, Year, Track#, Title, and embedded artwork. The radio wants to see additional things like ISBN numbers and such.
I used a free batch tagging program called MusicBrainz Picard. It was a bit painful, even though a lot of it is automated, because I still needed to go through every album and select a US release version to get the appropriate additional tags. The nice thing about that program is that it has a picture of the album art in the corner that seems to be correlated from the same database that Gracenote uses.. For example, you might be tagging an album like Pink Floyd's The Wall and notice that the album art picture is blank. If you go to the "release" information, you'll see that the album has been released many different times in many different countries on many different media formats. If you select the US CD release version, the artwork will pop up in the bottom corner, and then you know you have the right one. Save the tags that way, and it will show up on the car's screen 99% of the time.
Once the music was tagged absolutely perfectly with all of the obscure information, there still may be additional work needed for the artwork to show up - which is why I decided to branch to a 2nd music library. The radio can't display compilation albums correctly, and it also has trouble with tracks with guest artists and multi-disk releases.
On multi-disc issues, using The Wall album I mentioned earlier as an example, you would also need to manually tag the album names for the 2 individual CDs as "The Wall [Disc 1]" and "The Wall [Disc 2]" in order for the artwork to show up on all of the tracks. Any multi-track album must be tagged as if each disk was its own album by itself.
Compilation albums must be tagged as "Various Artists" for the Album Artist name AND Artist on every track - which sucks because you won't see who the actual artist is on the radio screen. If you don't do this, an album with 10 different artists will show up as 10 individual albums on the radio - and none of them will have artwork...
Any track with a guest artist must be tagged so that it matches the album artist, or it will also show up as a different album with no artwork. A John Smith album that has a track with an Artist tag like "John Smith feat. Joe Blow" must be edited so that it is simply "John Smith".
There was some artwork that I got a laugh with once I got most of it working in my car. Some of the artwork was a bit odd, like there was a Beatles album that had a very tiny picture of the CD artwork, a t-shirt, and a booklet that came with the album, like it was a promotional picture. I also had a few that were upside-down or sideways.
I've got a '16 now, so I'm pretty happy that the new radio systems can just get the album artwork from the embedded images in the file. I spend WAY too much time getting artwork on my radios...