which doesn't happen as often as you imply.
What happens is that 3-4 methods are used, the results are wildly different, and so the person tests it asks "what fossils do you see in the layers above and below this sample?", and the "indexing fossils" are used to determine which of the radiometric tests to use.
You meant to say: What has been reported, on occasion, is that..."
Sure, no method is fool-proof, all are subject to errors depending on circumstances.
When several methods -- including indexing fossils -- can be used to produce similar results, then the data is more reliable.
This is especially true when the ages of those "indexing fossils" were confirmed by several different radio-metric methods.
But those who use all this to argue that therefore the Earth is only 6,000 years old, are in no sense being scientific.