We keep seeing this misleading phrase. I’ve seen it dozens of times, in various forms in the last hour, repeated in mainstream media
Radiocarbon dating by three separate laboratories showed that the shroud originated in the Middle Ages.
Facts: One sample was cut and apportioned to the three labs. They all performed the same tests and, as expected, they got the same results. Three labs does not add to the validity. So, if three labs tested a sample that was cut from a medieval patch, three labs got the same erroneous result.
Robert Villarreal, of the Los Alamos National Laboratory, pointed out that
the  age-dating process failed to recognize one of the first rules of analytical chemistry that any sample taken for characterization of an area or population must necessarily be representative of the whole. The part must be representative of the whole. Our analyses of the three thread samples taken from the Raes and C-14 sampling corner showed that this was not the case.