People were absolutely aware that Mazovian aurochs are the last of their species. Jędrzej Święcicki have written in mid 16th century Topographia sive Masoviae descriptio (Topography or description of Mazovia, published in 1634), in this book he included one of the most valuable descriptions of aurochs:

In Jaktrów forest one can find herds of enormous aurochs. They are restricted solely for kings: under penalty of death no one is allowed to kill them. In ancient times, the animal had its habitats in the Germanic forests, nowadays (as far as I know) nowhere in Europe occurs, can be found only on this small patch of land, which is a remnant of the ancient Hercynia

Earlier (1565) papal legate to Poland Fulvius Ruggierii have written that aurochs "are to be found only in the Mazovian forests near Rawa, there are not many of them in Prussia". Venetian envoy Hieronymus Lippomano (1575) also noted that "They say that aurochs can be found only in the forests of Mazovia, where they are guarded and keep for the king's hunts".

Aurochs were restricted only for monarchs, we know about the laws from XIII century issued by Mazovian dukes that prohibit hunting on aurochs, and reserve them only for dukes. Polish kings and Lithuanian grand dukes were doing the same in their possesions and in Mazovia when it was included into Poland in late 15th century.

Peasants living in surrounding villages were obliged to take care of the forest and especially of the aurochs. Their responsibility was provide them enough food, some of them called łowczy were responsible of fighting off poachers. They were free from any other obligations, tributes or servitudes. At first it was just to keep royal herds intact for hunting but since 16th century it was mainly to keep the species alive (similiary protected was żubr - european bison). There was also other factor, tur/aurochs was regarded as national symbol and pride of the kingdom. When king Sigismund III was granting to Stanisław Radziejowski the position of starosta of Sochaczew he reminded him to:

Do his best in breeding of aurochs, not sparing any efforts and keeping guards in the fields, because they belong ad famam Regni, it is to the fame of the Kingdom

Aurochs or their horns were often granted as gifts to distinguished guests or foreign monarchs, like emperor or pope. They often were also invited on hunting.

Since the half of 16th century aurochs were counted so we know exactly how many of them were still alive. It looks like royal warnings were not enough because during first years of Radziejowski rule almost all animals died out (from 24 in 1599 to just 4 in 1602). Radziejowski was tried by royal judges, but eventually he remained on his position. His fault was evident but it looks like the herd was already so small that basically condemned to extinction.