While I prefer to think of Deckard as human, you've cited the "continuity error" that has bugged me since the first time I saw the movie. We've got four definite replicants: Batty, Pris, Leon, and Zhora. Deckard makes five. Who's #6? It's not Rachel, since she's Tyrell's special replicant.

Also, I think I recall in one of those numerous director's cut versions, the two missing replicants are explained away, but I can remember where or how.