Hi,
A lot depends on the source of songs in your library. If they have been ripped from recent CD's, downloads from Amazon, 7 Digital etc have a very high possibilty of matching all tracks per CD. Some track will not for some unknown reason even though they are clearly available in itunes.
Olders CDs from 80's may happlily match but with the release of remastered versions, the chance of complete matches are reduced
If you have vinyl rips, a lot will depent on the quality whether they"ll match or not.
I have a large collection of music. Excluding Purchases I have around 82/83% success rate. The 10% of the non matches are just not available in digital format. A small number have versions in itunes store but don't match because the length of my version does not match the itunes version.
Jim