My entire music library (45gb) fits on the card, yet much of the music does not show up on the device.
Then why, if you have sucessfully transferred 45GB of music to the card, do you say it’s only reading 32GB? Sounds like it working to me. More likely is the fact that the Clip+ (and all Sansa players for that matter) have a database limitation, which you have probably exceeded. That’s why it’s not seeing or displaying some files.
If I recall correctly the database limit on the Plus model is +/- 5000 tracks, depending on length of titles, images embedded in the ID3 tag and other criteria. If this is the case, and you’ve exceeded the original firmware’s design, the only option to you (in order to utilize the full capacity of the card) is to install and use Rockbox (3rd party) firmware.