Meh. Perhaps not fail, but become another 'lost' art...
For all we know, penicillin has been used many times before, but the knowledge of it failed to survive the ages.
You're right. The Principle of Self-Consistency only requires that recorded history not be changed. So a "lost art" would not violate the Principle, as long as recorded history was not changed.
So I suppose you could discover penicillin in the year 1015. And you could cure folks. But you could not cure, say, a king who was recorded to have died at a certain time.