It can be tedious, but you can also find new tables introduced/added through the release notes for service packs, hot fixes, and even product specific release note (e.g. CEM if I recall).
I know there were additional tables added to the schema throughout the 7.5 lifespan for CEM troubleshooting. I even ran the difference on the # of tables and views Pre-SP1 and Post-SP1 install - and if I recall the delta (or difference in tables) was only something like 20-30 added.
I have some documentation I tried to keep about the number of tables being added (and removed), I will see if I can find it.