Arrowheads were not particularly rare or valuable. Smaller points can be made in 5-10 minutes by experienced knappers. The shaft and fletching take a bit more work, but any war group would have been constantly producing them.
I always hated recording knapping sites because the thousands of lost or partial pieces that they just didn't care to pick up are a pain to document.
But if an enemy is unable to prevent the victor from pulling an arrow out, it's both more merciful and less risky to the arrow and the victor to deliver a coup de grace with a knife, axe, or club.
If that were the answer, why would anyone have recorded that the event took place? Reusing arrows would be common, and no particular arrow would be memorable enough to know you shot someone twice with it.
I always hated recording knapping sites because the thousands of lost or partial pieces that they just didn't care to pick up are a pain to document.