A restart of the client does typically cause it to check in and notice if things have changed for it to gather, but not send a Full Report.
You can deploy an action to a client to cause it to send a full report using the following actionscript:
notify client ForceRefresh
Right clicking on a computer in the console and choosing Send Refresh sends the client a UDP notification to send a full report. This will only work if the client is awake and can get UDP notifications.
The actionscript above does not have this limitation, it will happen when the client either gets a UDP notification to run the action, or when it does a poll for commands, or when it does a gather.
You need to be careful when forcing clients to send a Full Report. If this is done simultaneously to a very large number of clients, it could cause your root server and relays to get backed up with lots of reports to process if they are not fast enough to handle it.