Undesigned coincidences — definition and how they demonstrate historicity

An undesigned coincidence is when multiple independent accounts of an event interlock in a way that would be highly surprising if (a) the stories were invented, (b) one source copied from the other, or (c) both copied from a common source. The classic form: a question raised in passing by one source is answered incidentally by a separate, independent source. This provides evidence for genuine shared knowledge of real events — the hallmark of multiple independent eyewitness reports.