The second link (which no longer works 😟 ) used to tell you all bout it.
If on the computer itself you use any format other than WAV the information is also stored as metadata tags in each media file. Thus copying a media file from one place to another (such as burning to a data format CD) should see the information travel with the file (not play count or ratings or playlist data).
As long as a track is recognized as a current part of an iTunes library with an associated data file (mp3, AIFF, etc.) on the computer the data is stored in the iTunes Library.itl file too.
So, if you had the music burned to a CD in audio format (a regular music CD) and not in data format (won't work in many CD players), the data is not on the CD. If you only had the music on the CD the data wouldn't be in the the iTunes library file and I am thinking it may not have been in the CDinfo database (read my new link) if that is only Gracenote sourced CDs (i.e., ones from a commercial source, not one ripped from an LP by yourself even if the tracks were the same).
If you have a library file backup from the time you burned the CDs we can try working with that and see if it can help. It will still be some work but depending upon the number of CDs it may be easier than hand entering everything again.
