AA derives the FND User Name using an EBS function that captures the value from the database session that initiated the transaction. This value is to be considered extremely accurate and reliable.

The last_updated_by value is captured from the LAST_UPDATED_BY column in the table being audited. This column is usually populated by the form, page, concurrent program, or other logic that initiated the record change, however it is not automatic and relies on the programmer of that code to have followed the Oracle Development standards and guidelines.  Thus, this value is not a reliable indicator and is actually incorrect a small percentage of the time.

However, when these two values clash, it could also be the result of someone making changes from the back end with a SQL utility or a customization and forgetting to set the last_updated_by column.