Here's how it breaks down:
(CBI = Cannot be Interrupted, CBP = Cannot be Prevented, CBN = Cannot be Negated)
If I play a CBI, you can't stop it after it's played, but you can stop it beforehand (with say, The Strong Angel)
If I play a CBP, you can't stop it before it's played, but you can stop it afterward (with Five Smooth Stones, etc.)
If I play a CBN, you can't stop it before or after.