Introduction. The authors analyze previously unknown documents of the Russian archive of Jan Sapieha dating back to 1608–1611. Methods and materials. In the course of the study such methods as archaeography, paleography, historical and linguistic source studies were applied. The published materials complement significantly the fund of documents of the period and fill the existing “gaps” in available accumulated information in the preserved and previously published materials of the reconstructed archive fund, clarifying the chronology of events in Poshekhonsky and Uglichsky counties in the period from autumn 1608 till spring 1609 and expanding the scientific understanding of clerical practice in the Time of Troubles. Analysis. Two published newly found petitions of the mayors son of the boyar poshekhonets to False Dmitry II and Podorozhny, the only one of its kind that has come down to us, show that the possibilities of studying the archive of Jan Sapieha are far from exhausted. Results. As a result of the multifaceted analysis of the newly found materials, the informative value of the reconstructed archive was expanded, firstly, in terms of researching events that took place in lands that were located at a considerable distance from Sapezhin camps near Trinity and did not always fall into the field of view of the secretaries of the mercenary army leader; secondly, in the aspect of studying the genealogy of princes; thirdly, for the study of clerical documentation, including historical facts of changes in the order of promotion in the civil service of representatives of shabby families of service people during the Time of Troubles and the stages of development of business writing in terms of linguistic and documentary parameters of sources.