Third, some creationists like the members of the RATE group theorize there was a pulse of accelerated radioactive decay around the time of the Flood, but this would not apply to the post-Flood era.
Fourth, while it is true that we cannot know the past (this is the great limitation of experimental science), it is sometimes convenient to use the opposition's numbers against them.
There are two reasons uncalibrated dates must be mentioned: 1) this prevents people from making up any number they please, and 2) it is for the sake of posterity, where future scientists can check the results and apply new ideas of calibration. Radiocarbon dates are affected by many outside factors.
The accuracy of the machines is not in question (especially modern ones, which are astoundingly accurate when properly zeroed in). But, any source of old carbon in the ancient environment can affect the amount of C-14 in a sample.
Dendrochronology is used to determine variations in the C14/C12 ratio, but dendrochronology has assumptions that are not always valid (see bristlecone pine dating). Yes, a decreasing magnetic field strength would allow for more cosmic rays to enter the atmosphere over time, which would induce increased rates of 14C production and throw off any ancient measurement with respect to modern values.
And uncalibrated dates are usually only off by less than 20%. (1952) Radiocarbon dating, University of Chicago Press. C14 was originally calibrated using Egyptian artifacts of "known" age on the "standard" chronology. (1991) Radiocarbon Dating: Recent Applications and Future Potential, Quaternary Proceedings, Number 1, 1991, Wiley Even though this is not my field of study, I happen to have several of these in my files already.If that chronology is wrong, as many think, the calibration is wrong. But don't forget to compare to what is already available on creation.com: If you read articles like [note: link deleted as per our fedback rules], it is clear that the Egyptian dates don't always follow the dig.Note the clear references to a "plateau in the calibration curve" from 2500 to 2900BC, which would be due to the flood.
In the end, though, it seems to me there is little debate about the rate of decay in the historical era.