There is no information available about a Yervoy discount percentage on the provided sources. Yervoy is a brand name for the drug Ipilimumab, which is used to treat various types of cancer. The first source [1] provides information about the patent status of the drug, and the second source [2] is the official FDA label for the drug. The third source [3] discusses the high cost of cancer drugs, including Yervoy, but does not mention any discounts or cost reductions. Therefore, it is not possible to determine the Yervoy discount percentage based on the provided sources.

Sources:
[1] https://www.drugpatentwatch.com/p/biologics/tradename/YERVOY
[2] https://www.accessdata.fda.gov/drugsatfda_docs/label/2020/125377s110lbl.pdf
[3] https://www.reuters.com/article/us-usa-healthcare-cancer-costs/the-cost-of-cancer-new-drugs-show-success-at-a-steep-price-idUSKBN1750FU