I really don't think you know how DNA tests work.Why the DNA test is 100%?
it's the child's umbilical cord. Therefore the child's dna.(as stated above)
You just confirmed that Sarada is Sarada. That's it. If a DNA test is 100% that means you are the same person.
If Karin is the mother, and her DNA is being tested against Sarada's, then the test would not match perfectly.