The launch lists contain citations for each launch. The citation chosen provides evidence for the existence of the launch and its time. The second citation field, when filled, points to a reference giving further information such as launch vehicle type or payload.

The Refs file provides an index of the citations used. For some of them, it expands the cryptic reference code to something more like a proper citation; I'm afraid that for many that isn't yet the case. Get in touch if there is a specific reference you're trying to track down.