Some astonishing coincidences here. If Jankowski was indeed exiled in 1863 and married Olga Kuznetsova, from Buryat Kurtukov in 1877 then Michał Heronim Jankowski is NOT our man.
Attached find the Baptism and Marriage certificates of Michał Heronim Jankowski.
Date of baptism: 19 September / 1 October 1842 at 5 p.m.Father: Ignacy Jankowski, residing in Płock, age 36Witnesses: Antoni Kaniewski age 33 and Franciszek Kaszubski age 50, both residing in Płock Place of birth: PłockDate of birth: 25 September 1842 at 7 a.m.Mother: Franciszka nee Lewicka, age 38 Name of child: Michał Hieronim. Godparents: Józef Politowski and Urszula Nowicka
Date of marriage: 3 February 1867 at 6 p.m.Witnesses: Jan Wiśniewski age 31 and Stansisław Maruszewski age 60, both residing in Płock. Groom: Michał Heronim Jankowski, bachelor, born in Płock, son of Ignacy (deceased) and Franciszka nee Lewicka, age 25, residing in Płock – house number 359 Bride: Salomea Rybacka, spinster, born in the village of Krajkowo, parish of Zagroba, daughter of Szymon (deceased) and Marianna nee Smolińska, age 23, residing in Płock – house number 225. The banns were read out 3 times on the 6th, 13th and 20th of JanuaryThe couple declared that there was no pre-nuptial agreement.
The Baptism certificate of Michał Jankowski from the Polish Wikipedia site states: "In the town of Tykocin on the twenty-fifth of September in the year one thousand eight hundred and forty-two at nine o'clock in the morning. A nobleman, Jan Jankowski, a caretaker at the customs chamber of the First Office in Złotoryja, fifty-two years old, residing in Złotoryja, appeared. in the presence of Antoni Waszkiewicz, seventy-seven years old, and Józef Roszko, sixty-three years old, both hospital grandfathers from Tykocin, and showed us a male child born in Złotoryja yesterday at twelve o'clock at midnight from his Noble Wife, Elżbieta née Więckowska, forty years old; to this child at Baptism The saints celebrated today were given the names Michał and Mateusz, and his godparents were: The Honorable Mr. Jan Dobrzański, Clerk of the Customs Chamber of the First Office in Złotorya, and The Honorable Miss Julia Bardolewska. Assisted by: His Excellency Mr. Stanisław Walderowicz and Miss Aniela Bardolewska. This act was read by the Appearing Father and written and signed by Him alone. Both grandfathers cannot write. X Piotr Nowakowski, prob. Tykociński.