There are two ways to get hold of some DNA. The first is to get it directly, taking a sample of it either from a living body or a dead one. This has proven a tall order where Cryptozoology is concerned. Getting our hands on a body, any body, ain’t so easy as that. But Science has delivered a new way to obtain some DNA: environmental DNA extraction. Like, scientists can search through a body of water, like Loch Ness, and obtain from a sample of the water the DNA of the creatures that live in that body of water, then identify that DNA in the lab. That way they know what all lives in the water even if they never set eyes on the creatures profiled.
It works the same way with dirt. Nor is it something with a limited timetable. It is entirely possible to obtain a DNA profile of a creature no longer living in such a manner. Sometimes the profile of a creature that has been dead for a long, long time. Case in point: the DNA of a previously unknown population of human has been recovered from the dirt in a cave in Georgia (the former Soviet state, not the one Scarlet O’Hara was from) 25,000 years after the person died.