It is not difficult to see how such a claim could arise, however.
There are two characteristics of the instrumental measurement of radiocarbon which, if the lay observer is unaware, could easily lead to such an idea.
Measurements made using specially designed, more elaborate apparatus and more astute sampling-handling techniques have yielded radiocarbon ages for anthracite greater than 70,000 radiocarbon years, the sensitivity limit of this equipment. Continuous series of tree-ring dated wood samples have been obtained for roughly the past 10,000 years which give the approximate correct radiocarbon age, demonstrating the general validity of the conventional radiocarbon dating technique.
Several long tree-ring chronologies have been constructed specifically for use in calibrating the radiocarbon time scale.
Since no reliable historically dated artifacts exist which are older than 5,000 years, it has not been possible to determine the relationship of radiocarbon years to calendar years for objects which yield dates of tens of thousands of radiocarbon years.
Some organic materials do give radiocarbon ages in excess of 50,000 "radiocarbon years." However, it is important to distinguish between "radiocarbon years" and calendar years.In the early days of radiocarbon analysis this limit was often around 20,000 radiocarbon years.Thus, all the researcher was able to say about samples with low levels of radiocarbon was that their age was greater than or equal to 20,000 radiocarbon years (or whatever the sensitivity limit of his apparatus was).Long tree-ring chronologies are rare (there are only two that I am aware of which are of sufficient length to be of interest to radiocarbon) and difficult to construct.They have been slowly built up by matching ring patterns between trees of different ages, both living and dead, from a given locality.First, any instrument which is built to measure radiocarbon has a limit beyond which it cannot separate the signal due to radiocarbon in the sample from the signal due to background processes within the measuring apparatus.