By way of an update to those who may be following this thread I also has correspondence with FDA regarding the use of a date field in an audit trail as a data element and the editing of the audit trail through Data Clarification Forms. This is their response:

The audit trail in a part 11 compliant data capture system should automatically apply a date/time stamp to data elements entering the system. Modifications can be made to the source data and this is tracked by the audit trail. From your question it appears there may be linkage between the date as a data element and the date in the audit trail, which is not appropriate.
If a date in a source record is to become part of the data in the EDC, it should become a separate data element with its own date/time stamp in the EDC (See FDA Guidance Electronic Source Data in Clinical Investigations). Changing the audit trail based on changes in the source document would be considered a violation of our part 11 requirement.