Covert Art not in MP3tag file anymore

I just recently found MP3tag v2.43 and used it to add album / cd cover art to almost all of my 4000+ mp3's

I used and located each album cover and went to "Action" "import cover from file" and scroll over the the .jpg file and then i could see the artwork inside the mp3tag program

I then did most of my favorites mp3's and after that was all done i copied the mp3's to my xbox and can play them on there and see the album art at the same time

a couple of days later i was completing the art for the other mp3's MP3tag 2.43 all the cover art is now gone, anyone have a clue what could have happened?

"THINK" i found what i did, not sure why it happened yet, i went in and did a mass edit of the files and to remove track number of the songs and all the cover art dissappeared, if anyone knows why i guess i will have to start from scratch again