1)
Why does it say here "va'Yisyatzev
1.
Yerushalmi (Sanhedrin 12b): This teaches that he returned it entirely to the owner, and it was dear to him like [many fields, as if it was] a field full of saffron. Radak (16, based on Bava Kama 61a): David was told that as king, he may use others' property to save himself, or feed it to his animals; he refrained from doing so. 1
2.
Radak: There it refers to Shamah and Elazar. Here it refers only to Shamah, for he was primary in that war 2 .
3.
Malbim: The salvation was through all of them, including David.