I'm sure others will give a more detailed response, but I believe the answer is: a single timestamp of when the value was generated.
If the data is coming from a node with buffering enabled, there could be multiple reasons for the data to be 'late' arriving such as:
the buffered node lost communication with the data archive, the primary buffer on the buffered node became corrupt or data is being generated faster than it can be sent.
In previous environments, I've seen each of these scenarios occur.
If you want to determine the time delay between data generation and data receipt, find a 'busy' tag from the source site and create a new tag to record the time difference between the event timestamp and the value being received into the data archive snapshot system.