If the half buried SSCVR ULB was transmitting as specified the chances to be detected with available techniques and adequate methodology were very high.
I am very familiar with "weak signals detection" using DSP techniques,
intrinsically quite insensitive to noise.
In the picture below:
You have a signal that could be
IMPOSSIBLE to be heard and with proper techniques can be CLEARLY detectable in the computer screen (High Signal to Noise ratio) using widely available FREE software PC (Win) compatible.
For example:
With this setup you could tune in a distant NDB (impossible to be heard, even itīs carrier) and it will come up "loud" and
CLEAR in your screen
Another example:
You could have a CW 10W HF carrier operating in the 5 MHz* aeronautical band (dark hours) in the a/c, being monitored in DKR or REC with near 100% chances to tell you when disappear triggering an alert.
(*) 8 MHz in daylight.
Even with the current HF antennas (a/c and ground stations) very poor compared to the ones used by dedicated amateur radio in their stations.
PS
I will investigate what kind of Receiver they used in order to understand on their capability to succeed in cases like AF447.
And if the wreckage did fall in a hilly region it would be more difficult.