jcjeant, if the intent was not to find it, then they'd keep on not finding it, even though "they knew where it was." Simple. They'd still be "looking" and not finding it, today.
I do not find your dragging the conspiracy theory into the conversation, yet again, to be useful. The search kept on until successful ... with better equipment, and better techniques.
In other words, "they don't want it found" was proved a bankrupt argument as soon as "they" found it.