Umbrella sought to develop intelligent, powerful B.O.W.s that could be very expensive on the B.O.W. black market. Umbrella Europe developed the NE-alpha parasites back in the 1980s, but they were in small number and had low success rates. From all we know, the Nemesis-T Type was the only application of the parasite into a Tyrant's body. Since Raccoon City was destroyed, not much combat intel. was received from it.