In this scenario, the internal audit team's best course of action would be to thoroughly document the gaps in evidence that may have impacted the external experts' conclusions. They should communicate these gaps transparently to the external experts, providing additional context and information to help them understand the limitations of the evidence. By being transparent and collaborative, the internal audit team can work together with the external experts to address any discrepancies and ensure a more accurate and comprehensive audit report. Therefore, I vote for C. Recommend the external experts conduct additional testing.