In the determination of the laser-induced damage threshold (LIDT) of optical coatings former Round-Robin experiments stand as the empirical foundation for the development of the International Standard as it is known today. In 1983 and 1997 such experiments were conducted at the fundamental wavelength of the Nd:YAG laser under atmospheric conditions settling the International Standard as it is known today. To cope with the growing demand of LIDT testing for satellite missions, existing test methods have to be extended to deal with operation in space-like environments. This requires LIDT measurements performed under customized vacuum conditions to validate the laser resistance capability and estimate the life time of optical components. To foster the quality of measurements in such environments the need for an inter-laboratory comparison in vacuum conditions emerged.