Whatever. They want to continue using circular reasoning ~ the index fossils determine approx age of the rocks and age of the rocks determine approx age of the fossils.
So when blinded they can not re-produce their results - how telling is that!?!?
No circular reasoning involved.
First, I question the validity of those allegedly "blind" tests.
I suspect of necessity a certain amount of deception involved, and the labs were not fully aware of what they were being asked to do.
Second, the obviously correct analogy is forensic science -- the analysis of crime data.
You would never ask even Sherlock Holmes to interpret evidence from a crime scene without understanding the full context in which that data was found.
Yes, a "blind" scientific test is appropriate under some circumstances, but whenever you do one, you must control for every known variable and this, by definition, is not possible in random material of unknown origins.
So, with many variables involved in radiometric testing, all must be understood before results are relied on.
Plus ideally, results are confirmed by multiple radioactive materials, and by geologists' understandings of the rock strata they are working on.
If nearby rock strata include well known and previously dated fossils, so much the better.
So, yes, known fossils can help confirm rock dates, but only after those fossils were previously dated using radiometric analysis of the rock strata they're found in.
That is not circular reasoning.