Clear Install Flag

So, I did some investigation.
Some of those resources, which used to be installed have the heartbeat discovery date months ago, some about year ago. And still I know, that those workstations are in use every day.
As far as I understand this issue now:
Heartbeat Discovery DDRs are generated on clients during their refresh cycle. The client refresh cycle runs when you start an SMS client, when you update the SMS client configuration by using the Systems Management icon in Control Panel, or every 25 hours.

So, if user comes to work in the morning and after office hours turns power off. So, I think I must forget the heartbeat???

The clear install flag clears the install flag when clients are not discovered by heartbeat. when the sms client box is installed its set. You need to set the client rediscovery period to an interval longer than the heartbeat schedule.

AS you know a client is never going to un-install itself, so by deduction based that they were once clients I'm guessing they are either not communicating with the sms server or someone figured how to uninstall or prevent them from sending in information. (firewall for instance)

I would also take a good look at to see if perhaps they are somehow subnets were changed (are they not assigned either)

And really the most simple way is to take a look at the client logs that arent talking. Locationservices.log Clientlocation.log probably the exemgr etc