This makes me really curious about the origin of these early bows.
At that point in Chinese history there wasn't so much a unified cultural or political identity, it was more like warlord states with different groups. Since each of those groups would have had non-Chinese tribes and peoples in and near their "state" they may have received material tributes from satellite tribes or groups. Or even some exchange of craftsmen/workers.
Just imagining/speculating here, but given that likely mixing and interchange, maybe there were bowyers and bows of lots of different types. That brings up lots of interesting questions about progression of the bow and exchange of technique and technology, which may be represented in some of those pictures leehongyi shared.
I have nothing solid to back it up, but it may be reasonable to guess that the construction of the bow was standardized after the Qin Dynasty (something like 200 BC). If that were the case, that would make these pre-Qin bows even more interesting.