How did silver and jim know the treasure had already been taken?this is in part six.
In my opinion, it is quite clear that Long John Silver, at least, does not know that the treasure has already been taken (by Ben Gunn) by the time that he and the other pirates make it to the place where the treasure was buried.
To me, the main proof of this can be seen in what is said right at the start of Chapter 33. At that point, the men have just gotten to the place where the treasure was buried and have found that it has been gone for some time. The narrator says
THERE never was such an overturn in this world. Each of these six men was as though he had been struck. But with Silver the blow passed almost instantly. Every thought of his soul had been set full-stretch, like a racer, on that money; well, he was brought up, in a single second, dead; and he kept his head, found his temper, and changed his plan before the others had had time to realize the disappointment.
This proves that Silver did not know until he got there. It says right there that he was just as shocked as any of the others -- he had his heart set on the money. So he could not have known it was gone.