I used a different program called "Tagscanner" for a while before I found this program. I have found this one to have additional valuable features, and will be using it from now on. I do have one concern or problem.
I used the previous program to tag everything, including artwork. I use iTunes, and the album art is shown in iTunes. When I attempted to "extract cover to file" I found that many of my album arts did not get processed. Then I did a scan of my library and found more than half of them have a blank value for "cover" and no artwork displayed. I also get the "ID3v1 (ID3v1 !BAD ID3v2)" in the tag column. I have found that if I do anything like a save, it removes the art that was there and visible in iTunes.
How do I get it to "see" the artwork so I don't have to go get it all again? We are talking about 7000 tracks. No fun.
If itunes still has the data in its own database try to use the itunes function "Convert mp3 tags" and select a tag version 2.3 (not 2.4) even though the files may have the tags of that version in them
Then itunes will attempt to reconstruct the tags from its database. Perhaps even successful.
(as always with such a piece of advice: try it with a small number of tracks first. If it works: fine! If it doesn't: not too much harm done).
I did try the fix you suggested, but no success. I figured it out. Hope my post will help others who search similar issues.
Artwork was my biggest concern, it can take some time and effort to get it to one's liking. Since iTunes was showing artwork, I knew it was in there somewhere. I had Mp3tag setup to read all tag types, which was the problem. I went into Tools>Options and under Tags-Mpeg, I selected only one tag type to be read (such as ID3v2). I then refreshed the directory. I sorted by the artwork column and selected all that had a 1 and did a save, with all 3 types of tags selected to write. After that, I went back into the Tools>Options and selected only APE for read, refreshed the directory. Now there were more with a 1 in the artwork, looking good. Selected all with the 1 and saved again. Just for fun, I did this all over again, selecting only ID3V1. Eventually I got them all done, and the biggest delay in this was the refreshing of the directory (big library).
After all of the artwork was fixed, it was easy to see what other values were empty. Fields such as artist, album, genre were easily fixed.
Now I can get on with my original project of extracting the album art for archiving. That is why I started using Mp3tag initially. I certainly like that it helped me identify the failed tags, it just scared me when I thought I was going to have to retag everything.
Sounds like a solution by obscurity.
By the way ... the ID3v1 Tag cannot store any image data ... and you should avoid to use the APE Tag, because it has turned out that the APE Tag often leads into problematic situations when used together with the ID3v2 Tag.
Is there any reason to keep the ID3V1 and APE tags then? Would it save space to delete these tag types? What are the problems you mentioned?