This variable is the original intermediary control number (ICN) which is present on adjustment encounter, representing the ICN of the original transaction now being adjusted.
When an encounter record has been adjusted, the claim control number (CLM_CNTL_NUM) for the version of the record that is being adjusted appears in the CLM_ORIG_CNTL_NUM field – and then a new CLM_CNTL_NUM is assigned to this updated record. A null/missing CLM_ORIG_CNTL_NUM indicates that a prior encounter record has not been adjusted by the Medicare Advantage Organization (MAO). Generally, this implies that it is the first occurrence of an encounter service record, but occasionally, multiple record submissions for the same service may appear as original encounters.
Source: Medicare Advantage Organizations (MAOs)