I would say it means you need to document exactly when, how, where, who etc that you first personally saw (i.e. first hand) doing whatever it is you observed. For example, if I were to reference when I first saw a glass vase being blown, then I would refer to having seen a glass blown first in 2009, and then document the full reference as; 2009 M Jones, Senior Glass Blower, Waterford Factory, Ireland.
My academic field of referencing is nursing and health care so I could be wrong but it seems logical to me!
