[1] Tyszkiewicz was mentioned in surviving records for the first time in 1533 when received permission from the Grand Duke to marry Petronilla, widow of Glinsky.
[4] In 1929, Russian historian Matvey Lubavsky published an article identifying Tyszkiewicz as the author of Latin treatise De moribus tartarorum, lituanorum et moscorum.
[5] The treatise was published in 1615 and identified its author in genitive as "Michalonis Lithuani", which is often reconstructed as Mykolas Lietuvis or Michael the Lithuanian.
[6] However, Polish historian Jerzy Ochmański disproved the theory as "Michalonis Lithuani" identified himself as a Catholic and Tyszkiewicz was an Eastern Orthodox Ruthenian.
Ochmański proposed that Michalonis is not the first name but a patronymic on the verge of becoming last name and identified the author as Vatslav Nikolayevich (Vaclovas Mikalojaitis, Wacław Nikołajewicz), who served as a secretary in the Grand Duke's chancery for about 30 years.