They are guessing how much was there in order to determine the dates. Dating has nothing to do with how it is used in medicine.
If these radioactive isotopes half-lives are
known, and they definitely are, and these discoveries and technologies are
used every single day in this country to save lives and prolong lives and make peoples lives better, then their accuracy…all the way around (including dating)…is accurate…!
God forbid that you (or someone you care about) get cancer. But if that happened, you’d likely lean into
this science for your health to hopefully prolong your life, make your life better, and maybe save your life.