Even knowing that the patch work is there, it takes close looking with a photomicrograph to actually see the differences in the threads of the sampled area. The newer threads are dyed cotton to match the older original undyed linen flax threads. The newer threads have an "S" twist while the original Linen has a "Z" twist and are slightly larger than the newer threads. It is even more obvious comparing the threads under an electron microscope. The threads were not just interwoven, but the ends were twisted together in the "French Invisible Reweaving" technique with the idea the repair would be invisible to the naked eye. It was and is invisible.
May I ask the source of your information?