In my reply in the other thread, I think I gave you all of the notification types intrinsic to vB 4. You would then have to look at your "user" table to see if any of your installed products have added any of their own, such as "DragonByte Tech: Advanced Post Thanks / Like (Pro)" does.
Then once you have determined all of the notification types on your site, you would add them all up to get the total.