Old wood problem radiocarbon dating
If the spear head is dated using animal bones nearby, the accuracy of the results is entirely dependent on the assumed link between the spear head and the animal.
This is perhaps the greatest point of potential error, as assumptions about dating can lead to circular reasoning, or choosing confirming results, rather than accepting a “wrong” date.
Likewise, different living things absorb or reject carbon-14 at different rates.
For this reason, it’s preferable to date objects using multiple methods, rather than relying on one single test.
As samples get older, errors are magnified, and assumptions can render carbon dating all but useless.
For example, variations in greenhouse effects and solar radiation change how much carbon-14 a living organism is exposed to, which drastically changes the “starting point” from which a radiocarbon dating test is based.
So even brand-new samples contain incredibly tiny quantities of radiocarbon.
Eventually, the amount of carbon-14 remaining is so small that it’s all but undetectable.