When you are connected to the internet you need to search for the media information. Tools menu Options then Library tab and tick the "Retrieve information from the internet." This should correct the issue if these were previously identified. (It may take some time if you are on dial up so leave it running in the background but you must have a live internet connection.
If this doesn`t work and you know which albums these came from I suggest you create an album name for each and move each file manually (Drag and drop) so you have three seperate CD`s. Then right click a track and select "find album info" - then search on the internet to find it.