That’s been debunked. The sample used in the carbon dating test came from an area that had been patched. Microscopic views of that particular area showed a much different material pattern than the rest of the shroud.
Actually, no. The skilled reweavers replicated the weaving pattern and the color by dying the threads they were weaving into the damaged area to match the original cloth. There were discrepancies to the original cloth but they were not visible to the naked eye. These discrepancies were, however, visible under ultraviolet light because that area of the Shroud fluoresced while the rest of the Shroud did not.
This was due to the different chemical make up of the fullering, retting, and dyes used to make the patch threads match. Also, the dyed cotton threads were, on average, just slightly thinner overall than the average size of the Linen threads of the main body of the Shroud. The biggest difference was that the threads in the patch were an "S" twist, while the threads of the main body were an opposite "Z" twist. The opposite twist is apparently to better allow the joining of the threads together, so they will lock. At least that's one weaver's explanation. The weave pattern of the Shroud and the patched area were both three over one twill.