First of all I have so far received 4 positive antipoints and 2 negative. The Antipoints system first of all says that I have 70% negative and 30% positive.
Maybe the negs were a bit stronger than the positive antipoints you got. The percentage scores are for the actual number of antipoints you received, while what you see as 4 positive antipoints and 2 negative antipoints are the number of assignments you received.

Secondly the first three antipoints I have received have a date of 12-31-1969.
Simply means that the posts they were assigned to have since been deleted.

Hopefully that explains why you're currently on -27.