iTunes tracks not keeping metadata changes/artwork changes

I create music, make my own tracks and add them to my iTunes so I can enjoy them on my devices. (I do not use the cloud for music.) At some point, I changed the naming convention I use for my tracks. Instead of 11-18-07, I changed to using 20071118 so they would naturally sort by title. I have a bunch of tracks that still have my old naming convention, so I go to Get Info and adjust each of the titles. When I click OK, the track appears to get updated.

I also use the same image for all of my tracks. But some of my tracks, usually the same ones with the wrong naming convention, have messed up artwork - only a portion of the image is visible. So I go to the Artwork tab, delete the image and paste a fresh copy of the image. I click OK and the track appears to be changed.

Now here's the weird thing. If I go back to Get Info for one of these tracks I just edited or try playing it, it will immediately revert to the original version of the meta data and the artwork, as if I never changed it. I have done this a number of times. I get thru the whole list of tracks that need fixing and I think I'm done, only to discover on a later date that they all reverted back to the pre-edited version.

I tried going to the Media folder Get Info to set my ability to Read/Write on all files in the folder, but that didn't help. And I made sure they weren't locked.

How can I fix the meta data and artwork on these tracks? iTunes is not cooperating.