Uploaded songs to Google Play don't show up on Android device I'm sure this one is just a PEBKAC error, so please bear with me since I am new to Android.

I've uploaded all of my music to Google Play Music and I can see all of my songs via their web interface.  However, on my Moto X, there's at least one song missing.  I have tried refreshing the Google Play app on the phone to no avail.  I haven't had time yet to go through all of my hundreds of albums to see if any others are missing songs, as well.  Any thoughts?
Did you use the "Refresh" option in the google play music app? You can find it in the  action bar menu. Another possibility is a wrong file type. Here is a list of supported file types: https://support.google.com/googleplay/answer/1100462?hl=en