the stains on the Shroud totally match the Sudarium. The Sudarium’s history is very well documented. The Sudarium gives the Shroud even more credibility.
The Sudarium of Oviedo has a provenance which goes back to 570 CE, or about 1,000 years before the Shroud of Turin is first reported to be in Italy. But the supposed DNA and blood match between the two tends to disprove any conjecture about the Shroud being the creation of some medieval genius artist (so clever that his work left no paint or pigment but only discolored the fibers a few molecules in depth).