It has been proposed that the gravitational wave events GW170809 and GW170814 , named after their date (5 days difference) were actually a single one which appeared twice and magnified due to gravitational lensing. Both events have very similar parameters and come from the same area in the sky. Twin LIGO/Virgo Detections of a Viable Gravitationally-Lensed Black Hole Merger Some good discussion on reddit More generally, the authors of the paper argue that most of the observed events could come from lensing. It would mean the sources are smaller - they would fit to the mass range of stellar black holes we know from other observations. It would also mean they are farther away. Due to the way LIGO/Virgo work we don't expect to see multiple images often, but they should still happen. Future observation runs will easily distinguish between these options. If we see more repetitions then this is probably the case, if not it is probably not.