EB says there could be lots of Buddha statues out there: these large statues are not that rare and they're well recorded in many historical journals of people who traveled in the area. There are several reclining Buddha statues recorded in North India which have never been found. (Why has nobody found these if they exist?) If this sculpture is like others one, it's actually the same materials as the cliff face. So unless it's painted, to a casual observer it would look like another part of the landscape. And then suppose that over the years, a few wars and earthquakes have knocked off some distinguishing features, the statue could be well obscured. These valleys are also quite narrow and not easy to view. (Makes it perhaps easy to understand why Osama Bin Laden has not been found yet.) Absolutely. There's also the real possibility that, every time the mountain has shaken even a little bit from this prime earthquake, I don't think it's impossible that everyone would miss it.