Not necessary, because “trade value” has no relationship to the reasoning of the argument. If the tools did have trade value...that just opens the possibility that the tools could have been traded for other goods. Maybe the Aboriginals obtained the tools through trading? That doesn’t undermine the reasoning.

Necessary, because if it were not true — if the tools were NOT present in the region 5,000 years ago — then the fact we found the tools in that region would not provide evidence that Aboriginals lived in that region, or had access to the birchbark materials from that region, or had access to those tools in the region.

Not necessary, because the author’s reasoning doesn’t rely on the the specific purpose of the tools. We know that the tools are used to make birchbark canoes; whether the tools were designed to be used on non-birchbark materials doesn’t change the fact that we know the tools are used for birchbark materials. Also, “only” is too extreme — there’s no reason the tools couldn’t have been designed for use with many different materials, as long as the tools are still usable for the birchbark materials.

Not necessary, because even if there were other kinds of tools that were also used for canoe-making, as long as these tools were among the ones used for canoe-making, they still provide evidence of past Aboriginal canoe-making.

Not necessary, because even if these tools ARE known to be used for some other tasks in addition to canoe-making, that doesn’t change the fact that we know these kinds of tools are used for canoe-making among modern Aboriginals, and so provide some evidence that past Aboriginals used the tools in a similar way.

(A better version of (E) would say this: “The tools are not known to have been used by some of the region’s Aboriginal people exclusively for non-canoe purposes.” That version of (E) would be necessary, because it raises the possibility that the tools were used only for non-canoe purposes. But it doesn’t weaken the argument to point out that the tools might have been used for canoe purposes in addition to non-canoe purposes.)