I have been using Platinum Notes for a while now, but recently noticed the DB for my songs are not around the same. They vary from 92-99. It was my understanding PN normalize the volume for the songs it scans. Am I correct?
That depends on how the track was mastered. Metering often shows the "peaks" in the song, but it doesn't show the average volume.
If you process tracks using Sound Forge + iZotope (or Platinum Notes, which does the same thing), you'll get great results and the volume won't have to be adjusted between mixes. It's still an approximation, but it's much better than playing tracks from various sources -- their volume levels will be all over the place :)