A:

Failure to report costs in a previous period are also “errors” in reporting. So long as a full explanation is given, all adjustments for what ever reason can be included in adjustment for previous period.

But note; if the cost was not incurred in the previous period it is a cost of the current period. Some PO consider audit costs are costs of the “next” period (except the final period) and not the reporting period. There may be other similar costs that “bridge” two periods. e.g. a trip that starts at the end of period one and ends at the beginning of period two; or hire of equipment for a period starting during period one and ending in period tow. Reporting these in period two is correct and not and adjustment (of a proportion of the costs) to period one.