If a review of records can not provide a clear root cause,instead of providing corrective action for every potential issue that can affect inventory, consider implementing a cycle count program and use that as the stated corrective action.
The purpose of cycle counting is to identify how discepancies are being created within your inventory management system and apply corrective action.
Start by creating a "control group" of parts to count on a daily basis.
Criteria can be parts that historically have a lot of adjustments.
Make sure to establish a good daily inventory cut off (where transactions and physical movement is frozen) then count the same parts every day.
When an error is found, you then know the root cause of the error occurred no more than 24 hrs ago. This makes it much easier to research and find the real cause of that discrepancy. Over a relatively short period of time, this will give you the a good idea of everything that is impacting iventory accuracy.
As problems are identified and corrective actions applied, inventory adccuracy will improve. This is the systemic corrective action for discrepancies.