iTunes remembers what CDs it has seen before by storing the information in a file called CDInfo.CIDB. It is located in Appdata, not in your iTunes library.
If that file has gotten deleted, or if you have changed computer since the original import, iTunes will not "know" that it originally imported those files.
Has anything changed since you did the import?
OK, not clear where the file may have gone, but I am a little confused about what is going on. Are you saying you imported from CD at one time, did not get track names but lived with it, and now you have moved house and want to get the track names?
At the time you originally imported, did iTunes "recognize" the tracks on the CD?