With the history of partizan bias displayed by the testrers so far, I would hope that the Church does not allow every nick dick and harry to “test” the Shroud. I have much greater trust in the Church than in the habitual liars in the scientific community. Just look at the climatologists. I would not buy a used car from these shysters.
The chain of custody is obviously not clear, but the fact that the techological process that had produced the shroud has not been identified, and every indication is that it is from pre-medieval Palestine and displays the pathologies of the death by flogging and crucifixion, and burial according to the Jewish custom of the time convince me.
That another carbon dating will show some spectrum outside of 1 c would not prove anything, on the other hand, precisely because the chain of custody is not known. The first time they were looking at soot from a fire that occurred in the Middle Ages. Next time it will be something else like that. It is not terribly relevant what carbon dating will find.
Of course, there are relatively simple solutions to the problems you raise. So let me suggest just a few.