What type of proof would be required by an investigator to verify that a supplier has been designated an approved supplier? Would he or she ask for copies of audit reports if audits were performed?

Section 7.3 of Q7A says that supplier approval should include an evaluation that provides
adequate evidence that the manufacturer is going to consistently provide material meeting your
specification. That certainly could be a past history of incoming materials. It could include an
audit, but Q7A does not have that expectation. One should be prepared to share the information
on which you based your approval.