Grand Canyon seems to have a fair number of these situations. About a week ago, they received a SPOT 911 alert. When the ranger reached the group at dawn the next day, everyone was peacefully asleep in their tents.

It seems that a member of the party, awakened by what seemed to be signs of respiratory distress from the leader's tent, punched the panic button and then went back to sleep (!!??)

I'll bet that backcountry parties at Grand Canyon are now asked if they are carrying a PLB, and probably receive some guidelines on its proper use. Popular parks like Grand Canyon see wide ranges of skill and experience in visitors.