iPhone 5 sync question

First of all, I tried googling but every reply is either so complicated as not to be understood or they don't seem to answer the problem I have. I have an iPhone 5 and I tried syncing some music on my pc using the cloud feature. However, there is one album which I purchased which has 40+ tracks but after syncing, only about half showed up on the phone. Do I have to physically connect the phone to the pc and somehow force the files to sync to the phone? Is there any reason why some files won't sync? (I have a wifi connection at my house, btw.)