A recent South Korean press report about the possible defection by an official working for a North Korean bank that provides funds directly to the Pyongyang leadership set off a flurry of speculation about a potential trove of information about the financial operations of the regime.

Information from significant defectors often remains out of the public domain, however, as intelligence services limit the release of testimony from high-level exiles. The paucity of first-hand information from senior North Korean officials is...