The most common reason for such episodes is that a student takes a job before completing a thesis, usually after attaining ABD (all but dissertation) status. 2001, John Siegfried, Wendy Stock, “So You Want to Earn a Ph.D. in Economics?: How Long Do You Think It Will Take?”, in The Journal of Human Resources, volume 36, number 2, page 366:
Most of my employers knew I was a graduate student, and fortunately, most seemed reluctant to ask me too many questions. Our mutual silence served as a way to deal with the status inconsistency of a house wife with a B.A. hiring a ABD to clean her house. 1992, Mary Romero, “Intersection of Biography and History: My Intellectual Journey”, in Maid in the U.S.A., Routledge, →ISBN, →LCCN, page 6: