Note on slide 10, audit information (1):

Adding audit information for delete operations is good.

Instead of recording the whole SOAP message and the cryptographic signature,
you could get away with the ID since the URs are always stored in a trusted
storage.
Usually you also do not expose audit information via the Web-Services interface.

A suggestion would be to put the audit information inside of the UsageRecord.
The current createdBy and timestamp elements in the UR are meant to document
the actual creation of the UsageRecord itself, not the insertion into a RUS.
Probably audit information elements could be added to the UR.
That would mix data and meta-data, which is not a good idea.

extractRecordHistory is feasible.
One should be aware of privacy issues associated with that operation. Not all
users may be allowed to see the whole audit trail.

It would be interesting to also consider reading as an audit operation.
Make it optional for RUS that do not want to record it.