"the search effort has been hampered by the reluctance of all parties in the region admit to what they have actually seen on radar."
To state the obvious, various countries in that part of the world don't want to admit that:
(a) the radars may not be operating all the time.
(b) they may have missed something even when the radars were operating.
For example, India was forced to admit that its radars around the Adaman Islands were not actually on all the time in order to save money.