In the OPC UA Part 11 (historical) contains sections describing Historical Data and separate section for Historical Events. In the Historical Data section the concept of Modified Values is addressed. In this section the specification details behavior with regard to historical values that have been edited. The concepts described include providing a manner to discover that prior values exist and to retrieve these older values (values from before they were edited). This retrieval includes information regard who performed the editing and when. In many industries it is critical that this older data be retained and that any changes are recorded.
In the new Historical events section, the concept of modified value is not addressed. Interface are provide to allow editing, inserting, updating and deleting historical events, but other than the standard audit event indicating the action has take place no additional behavior is defined. In most industries tracking changes to historical event is even more critical than historical data items and the specification should be enhanced to include a description of behavior that is very similar to Modified Values except that it is directed to Historical events.