What version and product have you you posted in other products so is this MAC or a corporate product or consumer. So I can move it to the correct area for you.
If it is the consumer version you can see the update date in the about link bottom right of the security Centre.
In consumer it is there in the registry as well but easier to use the about that is why I feel your question is not about consumer.
We are using mcafee antivirus enterprise edition and we would like to know how we can find out when mcafee antivirus was last successfully updated from command line or from registry.
Using the AVDatDate and AVDatVersion is mostly correct.
For a healthy system it will always be correct. But systems are not always healthy.
The most accurate method to check the date from a client, is to inspect the Application Event log for the most recent "Event ID: 500x" from Source: McLogEvent, where 500x is an Event ID of 5000 or higher.
For example, Event ID 5000 is logged whenever the scanner starts, and within the event it records the DAT and Engine version.
Any Event ID higher than 5000, is indicative of a problem with the scanner; details will be found within the event.
Therefore, look for the most recent "McLogEvent" Event in the 500x range.