I had the same issue going on my iPhone 5 (iOS 9.2.1) was such a pain trying to find solutions to get the right album artwork for the right songs...
But then i found a way in the end to retrieve the correct album artwork for my songs:
1. On your iPhone device:
Setting > General > Storage & iCloud Usage > Manage Storage > Music > Edit > Press [ - ] All Songs
2. Then open iTunes on your PC and connect your phone
3. On iTunes:
Press the iPhone icon > Press Music in the Settings section > Untick Sync Music > Then Sync > Tick Sync Music > Sync Again
I retrieved all the correct artwork for my songs by doing the same procedure twice but some of you may have to do it more than twice