A cyclotron is sometimes used for carbon dating
We know (from other measurements) that the Sun hasn't fluctuated by more than 10 percent in the last million years.However, even this small an adjustment was a bit of a shock.It is also standard to coat fossils during their extraction and transport.Acetone is sometimes used while extracting fossils, because it dissolves dirt. It is produced in the upper atmosphere by radiation from the sun.(Specifically, neutrons hit nitrogen-14 atoms and transmute them to carbon.) Land plants, such as trees, get their carbon from carbon dioxide in the air. The same is true of any creature that gets its carbon by eating such plants. Suppose such a creature dies, and the body is preserved.That causes a dating problem with any animal that eats seafood. After about ten half-lives, there's very little C14 left.So, anything more than about 50,000 years old probably can't be dated at all.
And, we can date things that have been dated by some other method.
See below for details about the 45,000 annual varves in Lake Suigetsu. For example, polar bears that eat seals aren't getting their carbon from an atmospheric source.
The second kind are datings on contaminated samples, or on samples which are a mixture.
It is sometimes possible to match up tree-ring patterns between different trees.
When enough suitable trees are found, living or dead, the matching is completely accurate.