Contamination is a legitimate and very real source of error in carbon-14 dating.
Sounds like the charge of ‘contamination’ represents a built-in escape hatch for the researchers to simply toss out any dates that don’t comport with their established thinking. Convenient! Nelson states in his book Dire Dragons, in the section dealing with the hadrosaur specimen he had tested, that decontamination was performed prior to testing. Don’t know what more you want here, but in the end you would need to provide actual evidence that his specimen had been contaminated. You can’t just claim it was contaminated because of your pre-existing assumption that dinosaur specimens are millions of years old. His specimen dated to 25,000 years before present using the C14 method.