I have this chord sheet of Cigarettes and Alcohol handwritten by Noel Gallagher in the 1990’s. With provenance from Jason Rhodes, Noel’s guitar tech during oasis years, and a nod from Noel’s daughter Anais. Is that good enough to confirm it’s genuine?
You'll need third-party authentication for such an item. Roger Epperson, PSA/DNA and JSA are the mainstream authenticators recognized by major auction houses. Otherwise, the documentation is a little flimsy on its own.