I think you mean 'verifiable' evidence. It's based on certain assumptions, one of them requiring consistent levels of C14 in the atmosphere but if the flood of Noah's days is a historic event, that assumption only holds good up until the time after that global flood. Relying on a gas in the atmosphere, and consistent levels of absorption so as to work out its 'half-life' (decay), is not a sensible way to judge dates.
With regard to radioactive decay, here is what an Analytical Chemist wrote. He was once a Licentiate of the Royal Society, specialising in chromatographic analysis of components down to parts per billion. He wrote of being "aware of the complexities of spectroscopic analysis; aware of the very unreliable methods of rock analysis; aware of the fact that sedimentary rock was definitely laid down in the aftermath of the Great Flood; aware of the fact that rock originates from that which may be molten; and aware of the fact that isotopic abundance is a mixed matter of creation, sedimentation and, only then, radioactive decay."