.....if the ELT can't be picked up, that indicates either that it is/was defective, or that the craft is sitting in some ravine somewhere.
Or if the ELT is underwater. But I don't know how much little water there is there.
In New Brunswick, Canada there was a small plane crash in a remote area for which the ELT turned-on 1 year later. They presume that possibly an animal had touched it somehow.
A commercial flight at -15 C, with ice on wings during TO, crashed into the St-Lawrence river; the ELT was under only a few feet of water. That seriously hampered emergency response and resulted in deaths.
It is not rare to hear that an ELT does not work as advertised.
I remember one activating on touch-down and jamming my conversation with the tower; of course during my early solo days
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