What does "!BAD" mean in the tag column

I am an absolute newbie to this stuff. I ripped all my CDs using EAC. When I opened these in MP3Tag to fix some of the tag issues, I see "ID3V1 (ID3V1 !BAD ID3V2)" in the tag column. Does this just mean that EAC only saves the ID3V1 info and the ID3V2 space does not exist??

Also, the first files that show on the list are AC/DC. I changed some tag info on the first song and saved the tag. For that song the tag column now reads "ID3V2.3 (ID3V1 ID3V2.3)". The Artist Info is listed as "AC/DC" in the MP3Tag file view, but when I look at the file in Windows Explorer, the Artist is listed as just "AC". Is this just a Windows problem?

Thanks, a bunch.

!BAD ID3V2 means the ID3v2 tag contains errors that make it impossible for Mp3tag to read it.
If you created all the files by yourself it is a little strange that you have got invalid ID3v2 tags.

"/" is used in some programs to separate multiple artist entries in ID3v2.3 tags.
Windows explorer will always treat AC/DC as two artists and can only display one.
Editing this tag with the explorer appends the new value to DC/
So don't use the explorer to edit these artists.

Windows Media Player has implemented it better, e.g if you enter e.g. "AC/DC" it writes AC/DC in the tag and will also show you AC/DC
If you enter AC;DC it will also write AC/DC to the tag but it displays it as two artists AC and DC

I did not create the tags. They were generated automatically in Exact Audio Copy (extracted from freedb, I think).
So maybe this is some bug in EAC.

Yes, I meant you did not download or copy these files from some unknown source. That's more likely to get corrupted files from.

Maybe you should review your EAC settings or check if there is some other program editing your files.