According to Marketo/Insightera's overview, typical B2B has thousands of prospects each month, 50-70% are new, and 98% are anonymous. Less than 1% are known and addressable. Obviously your situation could be slightly better or worse, depending on the size of your database.
I don't know exactly where they got this stat, but sat on an Insightera presentation yesterday, and that's what they said. Hope it's helpful!