15 less songs on iPod than iTunes?

All my music is set to sync to the iPod, there is plenty of storage available and I have checked for duplicates and there are none in the same album etc so surely they would still sync (a few are twice due to greatest hits albums or compilations but there are many more than 15 so this isn't the reason) I have 7,019 songs and my iPod claims to only have 7,004 and obvioulsy with this many it's hard for me to figure out which, if any, are missing. Any suggestions?