Just exactly what it says. The Shroud was repaired in some damaged areas by a technique called "French Invisible Reweaving". This technique has been seen on other cloth from the 16th Century onward.
The repairer makes a linen thread (in this instance with some telltale Cotton fibers spun into it that do not exist in the original Shroud threads), dyes it to match as closely as possible the color of the original threads, and then very skillfully weaves the new threads into the old, intertwining the old threads with the new.
Photomicrographs of the C-14 text patch clearly show the differing threads... especially since the newer threads have an S twist while all of the original Shroud material is made with yarn with a Z twist (opposite twist). The newer threads have been shown to be chemically different from original threads as well (R. Rodgers, et al) utilizing a Madder Root dye (no dye on Shroud threads), a differing fullering method, and a different bleaching method.
Photographs taken in ultraviolet light show that the area in question where the sample was cut fluoresces differently than does the balance of the cloth (B. Schwarz, et al) indicating that something is different.
Analysis of the one surviving sub-sample from the five that were cut from the single sample for C-14 test shows that the side closest to the left selvege of the Shroud are of the newer material while the material on the side toward the body of the shroud is of the older material. The change-over occurs on a slight diagonal area/line that moves from the right at the bottom (foot end of the Shroud) toward the left edge... with the percentage of New material to Old corresponding to the inexplicable (till now) variation in the test samples ages reported from the three labs. The ages reported from four sub-samples cut from the same sample varied from 1260 (+/-25) to 1390 (+/-25) with the ages of NONE of the samples overlapping the degrees of confidence of any of the others... This should have been a red flag that something was wrong with the samples as all three labs should have been much closer if the sample were homogenous.
The threads are not the same, ergo the C-14 test patch is not the same as the rest of the shroud.
Thank you very much for the reply. That was a very thorough and succinct treatise.