Virtual standby sync status

We have two physical servers that host the virtual standbys for all our virtual servers.
This works great.
But how do i know if they are in sync ?

For an example.
Yesterday a export failed.
I found the problem and forced a export and everything looked okey again.
But must i start the virtual standby to know if it's okey ?

One thing i have learned is if i start up a virtual standby and after shut down of it forget to revert to snapshot ,it does not work after next export.
So then it's not in sync.
I then have to delete the virtual standby and make a new one time export.
Can't this be made automatically ?

Is there a way to schedule a full export ?