Wookie Loyalty: Exhaust this card while you or an adjacent friendly figure is defending to apply +1 Block to the defense results .

results -> plural

Why? Can be used against more than one attack?

Results is the correct English in that sentence. You can have multiple results per defense roll. Since you have to exhaust the card it cannot be used again until ready.

Not for multiple attacks, I believe what they are implying is that the figure defending may have natural defense, plus additional from something else and you are then enhancing the defense result further.

I have not looked through all the crate cards but I would imagine there will be something in there that will no doubt enhance defense.