You state this was a recall formation. It sound like this was a last minute thing. If the Soldier did not know about the formation then he cannot necessarily be held accountable for missing a formation that he was unaware of.
However each Soldier is required to have a means to be notified. In this electronic age I am sure the Soldier has a cell phone. Even if the Soldier does not have a cell phone they are required to have a means of receiving emergency notifications if they live off post. Usually a neighbor willing to pass the message along for recalls, etc.