Spell X is not in the Spells Tab List
Addons can not just read a list and immediately know every spell in the game. The list starts out empty when you first install SBF, and gets populated as you go out and cast spells, and have spells cast on you. If a spell isn't in the list, you simply haven't cast it (or had it cast on you) yet. Don't forget there are buttons to the left to toggle showing buffs and debuffs.
Ah, okay, I'll just go do that then
Sure, you can just go cast it or get it cast on you and it'll appear in the list. Under the hood, though, the Spells tab is really just a convenient front end that writes some filters for you. As long as you know the name of a spell, you can make the filter for it just fine. When you select a spell name, say, Arcane Brilliance, in the list and check off that Show (or Do not show) checkbox, all SBFOptions does is write this filter: n=arcane brilliance. When you check off the Cast by me checkbox, the filter becomes n=arcane brilliance&my. If you check off the Cast by anyone of my class checkbox, the filter becomes n=arcane brilliance&c. Just click over to the Filters tab and write em yourself, no problem!
I hit the clear data button and all the effects in the spell tab went away. Halp!
Yep, the clear data button clears all of the cached spells. Your cache is now empty as if you had just installed SBF from scratch again. It'll fill up again nice and quick. Go shoot something and then play with it.