North Korea continues to push ahead in developing long-range missiles capable of delivering nuclear warheads to the continental U.S., conducting a landmark test of a solid-fuel intercontinental ballistic missile (ICBM) on Thursday.

But intelligence assessments in the recently reported leak of classified American documents raise questions about the DPRK’s actual capabilities and, according to experts, serve as a reminder that there are caveats to the country’s rapid progress in weapons development.