They leave the door open a little bit, but Jared Leto seems to be saying that Tyrell either made Deckard and Rachael as a matched pair of 'special' replicants for breeding purposes, OR that human Deckard meeting special replicant Rachael was Tyrell's plan. I don't think Leto really knows for sure either way. It's clear he doesn't fully understand how Tyrell did it. The wording about 'design' seems to make it intentionally ambiguous.
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