In the case of an audit there should only be a need to re-assay perhaps 5% of all samples as, taken randomly, this is representative. In fact this is a procedure that many companies employ as part of their QAQC programs.  Often after drill results are reveived the pulp from every 20th sample is forwarded to a second lab for assay - these are called check assays. If the original and check assay results agree with one another it provides a second level of confidence in the assay results.