Expect CLTC to be advertising the best possible range.
There's a ceramic battery hitting the market that has a marginally higher density and nothing is stopping them from adding more batteries. There's also a new hub-motor concept that has a lot less losses, but they're not car sized yet.
Getting to 644 would be as easy as throwing more batteries at it, but i'd expect those numbers to come down a bit, or the price to be much higher.