Does a patent's presumption of validity afforded by 35 U.S.C. §282 limit a district court's discretion to find a case exceptional under 35 U.S.C. §285 when it is only later discovered the accused technology is prior art?

QUESTION PRESENTED 1. Does a _ patent’s presumption of validity afforded by 35 U.S.C. §282 limit a district court’s discretion to find a case exceptional under 35 U.S.C. §285 when it is only later discovered the accused technology is prior art? 2. Given the clear and convincing evidence standard to invalidate a patent, does a district court have the discretion to find a case exceptional under 35 U.S.C. §285 based upon asserted but unproven grounds of invalidity and unenforceability?