How do I fix a squeaky carpeted floor given that scored screws don't help?
Squeaking usually comes from two places:


Joists.  Loose, overloaded, damaged, braced improperly, not even.  Fix is usually lateral support using crosses.  
Plywood.  Poor quality, warped/damaged, not thick enough, not glued down, not screwed properly or enough, pattern not well thought out (edges should be on joists or supports).  Usually have to pull them up to figure out the issue.  


In your case you don't want to open up first story ceiling so you need to pull up a couple pieces in high-squeak areas.  Figure out what the issue is.  If the joists aren't even (note that I didn't say level) the boards will eventually squeak.  If there is no cross-bracing then the joists certainly have movement which itself can cause a squeak but also loosen screws or make screw holes bigger over time.  These are just common examples.  You can keep adding fancy screws every inch but you don't know the root cause yet.