The U.S. and South Korea held the third meeting of their joint Nuclear Consultative Group (NCG) in Seoul this week, after establishing the group last year to bolster communication about how Washington will use its nuclear arsenal to defend against North Korean threats.

But while officials hailed the completion of a classified “guidelines document” as a “milestone” in strengthening extended deterrence, what little they revealed about the guidelines raised questions about a persistent gap in how the two sides understand the role of U.S. nuclear weapons in their military alliance.