He is mentioned in the book Zygmunt Heryng (1854-1931): Biografia lew icowego intelektualisty (2011) by Marta Sikorska-Kowalska. The book s ays that he has a family archive containng material about Zygmunt Hery ng and his family which the author used for writing her book. The fam ily photographs in the book come from Jan's private archive.
According to this book, Jan Koslowski is the son of "Jadwiga Balicka-K ozlowska" who is the "granddaughter of Zygmunt Heryng." Howeer, thi s must be a mistake. Presumably the author whould have written that J an Kozlowski was a son of "Helena Balick-Kozwlowska" since Helena wa s indeed a granddaughter of Zygmunt Heryng, and had the full surname o f Balicka-Kozlowska.