43mm Nikon filters
Most 43mm filters for Nikons were labeled "Nippon Kogaku" during the RF era. A few were labeled "Nikkor." It may be difficult to find any in that size with just the Nikon label. Remember, Nikon meant a camera back then, not a company.
Filters labeled "Nikon, Inc." are NOT filters made by NK. They were filters from Ehrenreich's importing company, designed to cover filter types that NK did not make themselves. They were actually made by Tiffan and are laminates, not dyed in melt glass filters.
Hope that helps, WES