A common misconception about radiocarbon dating is that it gives a precise date---3577 B. In actual practice radiocarbon dating can only give a range of dates for a given sample---3650 to 3410 B.C., for example---the true date lying somewhere in that range.
(For a good example of the role radiocarbon plays in biblical chronology see Is Bryant Wood's chronology of Jericho valid? Once such large-scale errors have been eliminated the precision of biblical chronology rivals that of dendrochronology. Radiocarbon is not generally useful for narrowing the range of such biblical chronology dates further because radiocarbon tends to have poorer precision than biblical chronology.
Radiocarbon Every day cosmic rays bombard our atmosphere.
These cosmic rays release free neutrons which zip around our nitrogen rich atmosphere at high velocities.
Thus it is possible in some instances for two samples from a few decades apart to have the same radiocarbon concentration today, and hence the same apparent radiocarbon age.
This happens whenever there is a wiggle in the curve at the time the samples died.