There is no evidence it has ever been used and it is perfect. Nikon released DIC with the release of the research scopes Optiphot and Microphot series 1 and 2. The lenses were specifically released for DIC as there were chosen for their flare free optics required in polarization and therefore DIC. They are also superb lenses for brightfield. While a Nikon lens, it will attach to an Olympus finite microscope with RMS thread.
Note they are 160 tube length so not useable on any of the infinity microscopes from E400/600/800 series and later. The item "Nikon Microscope Objective Lens CF Plan Achromat DIC 20x for Finite systems" is in sale since Wednesday, March 24, 2021. This item is in the category "Industrial\Healthcare, Lab & Dental\Medical/Lab Equipment Attachments & Accessories\Microscope Parts & Accessories\Microscope Objectives". The seller is "ozmicro" and is located in Bundaberg, QLD.
This item can be shipped worldwide.