In the late 2000s, for instance, rumors circulated about a bunker in Iran struck by a bunker-buster bomb. The bomb had failed to penetrate—and remained embedded in—the surface of the bunker, presumably until the occupants called in a bomb-disposal team. Rather than smashing through the concrete, the bomb had been unexpectedly stopped dead. The reason was not hard to guess: Iran was a leader in the new technology of Ultra High Performance Concrete, or UHPC, and its latest concrete advancements were evidently too much for standard bunker busters.

https://en.wikipedia.org/wiki/Fordow_Fuel_Enrichment_Plant

Construction on the facility started in 2006, but the existence of the enrichment plant was only disclosed to the International Atomic Energy Agency (IAEA) by Iran on 21 September 2009,[6][7] after the site became known to Western intelligence services. Western officials strongly condemned Iran for not disclosing the site earlier;

Seems to fall into the same timeframe.