Rachael is definitely referred to as a Nexus-6 in Blade Runner, even if she’s an experimental one. Deckard though, well, I’ve always thought that he was a new Nexus-7. Maybe the first Nexus-7.
And Nexus-7’s could easily have indefinite life-spans like the Nexus-8’s.
Who said he took his wife there when she was pregnant? Rachael died in 2021. Blade Runner took place in 2019. That’s two years that Deckard and Rachael were on the run together, before they separated.
They could easily have hid in Vegas, where Deckard acquired the wood, gone elsewhere and then after they separated, Deckard could have returned there at any point in the past twenty-something years.
If they were on the run, then they would have been constantly on the move, rather than hiding in one place.
Plus at some point they would’ve had to have encountered the Resistance, who were certainly not based in Vegas, since they had no clue where Deckard was.
Tyrell definitely can’t be trusted, if he even is Tyrell, it was the original intention that the Tyrell we meet is just a replicant, and that Batty would find another room containing a life support pod containing the real Tyrell after he’d killed the copy.
JF would then reveal that the life support pod had failed in 2013, and that the real Tyrell was long dead.
Like the scene with the Sixth Replicant Mary, it was cut because of a writers strike.