I would like to provide information if retrieved PI Point is stale. I'm already available to provide if Point is good. It will be fine, if I can also provide if PI Point is stale.
I'm using SNAPSHOT property of ListData object.
It depends on your definition of stale for the PI Point. The most simple approach would be to use the timestamp of the snapshot and compare against your stale limit, e.g. if the timestamp > 5 minutes then it is stale.
With ListData you retrieve all the snapshots and perform the above processing locally against each event. You may be better off using something like GetPointsSQL to only retrieve tags that are stale, processing is done server side.
Consider using the PI Interface Status Utility (ISU) as well...
Retrieving data ...