Album art and artist not showing

I am new to this so apologies if this topic has been handled. I have a GWM Steed 5 car/pickup with a very nice display radio/USB player. I have used MP3 tag and painstakingly gone through adding the album art, edit the name of the band and song. When I use the USB in the car it sometimes picks up the correct name and art etc but a lot of the time it will say unknown artist and no album art, What am I doing wrong.

I thank you for any advice

The files should have data in ALBUMARTIST, ARTIST, ALBUM, TITLE.
If ALBUMARTIST is not filled then the albums appear all to come from the same artist, the unknown one.

On the problem of the display of pictures, see e.g. here and check if anything applies to your player:

Thanks for the response. Turns out that the issue is caused by Gracenote -- there are multiple threads in various forums about this. It should be that if there is MP3tag information on local media, that should be what is displayed. But no. It seems that if there's any discrepancy, either Gracenote rules or it displays some generis photo. I have 1 album that displays something different than what it's tagged with, several tracks that have generic photos that aren't even related to the album or artist. There have been times when I've started my car with the stereo on a particular track and ti starts up fine -- correct album art and all. When the "Powered by Gracenote" line appears, the album art goes away. VERY frustrating, but there seems to be nothing I can do about it.