Usage in IPAP

@dave67 I assume my reply wont help you much but thought of adding some thoughts.

Last Year (Out) indicates the qty issued from the Inventory during the period. Therefore if the Transaction Codes are known for qty issued from the Inventory (all scenarios), it is possible to get the count from 

Warehouse Management\Transaction History\Inventory Transaction History per Part

Even though the related Transaction Codes can be found in the documentation under the topic Posting Types and System Events - Supply Chain and Manufacturing, it is not straight forward to determine which codes are considered for this calculation.

To get this value calculated, following job is required to be executed (in other words if this field is empty, then probably executing this job would solve the issue).

Warehouse Management\Transaction History\Aggregate Inventory Transactions per Period

Therefore to get the exact list of codes for this calculation, it is possible to check the underlying code for this job. It would be a complex code as it not only handles this calculation but this is the most accurate way to follow (if such requirement exists), IMO.