Violations of this assumption can frequently be identified.Three additional assumptions are necessary in radiocarbon dating in order to estimate the initial concentration of C could be caused by changes in the intensity of the cosmic radiation or in the strength of the earth’s magnetic field.The reasonableness of this assumption probably depends on the environment around the sample.A sample that is sealed from the surrounding environment is more likely to avoid contamination or loss than one in an open environment where materials may be carried into or out of the sample by water or simple diffusion.This ratio would have been different before the Flood. According to these authors, the total mobile (non-carbonate) carbon in the biosphere is about 40,000-45,000 gigatons. The global carbon cycle: a test of our knowledge of Earth as a system. The earth’s sediments contain a vast amount of carbon-12 in the form of coal and oil.  Post WM, Peng TH, Emanuel WR, King AW, Dale VH, Deangelis DL. The amount of carbon in fossil fuels is estimated at 6,000 gigatons, and the amount of kerogens (organic) in sediments is about 15 million gigatons.
Violations of this assumption occur in the ocean reservoir due to the time required for mixing of surface waters with the deep layers.A final assumption is that the various rates of flow of carbon-14 among the respective geophysical reservoirs must be constant, and the residence time of carbon-14 in the various reservoirs must be short relative to its half-life. (Riverside, CA: La Sierra University Press, 1997), 183. Carbon-14 dating models and experimental implications. Origins 24(2, 1997):50-64  The deep ocean waters are estimated to take about 1000 years to circulate back to the surface: Aitken, MJ. If these three conditions are met, the initial concentration of C in the sample can be estimated. C in coal and oil is much less than in the present environment. This gives a ratio of 300:1 for pre-Flood biosphere carbon to present biosphere carbon. If a significant portion of the coal and oil represents organisms that were deposited in a global flood, then the pre-flood atmosphere must have contained much less C over time resulting in wobbles and deviation from expected levels in the standard calibration curve based on samples of known age?  Note the wobbles in the curves in Pearson, GW et al. Evidence for correlations between nuclear decay rates and Earth-Sun distance – et al. This differs by a factor of only two from the figure of 143:1 proposed by Brown (Brown, RH.