Sometimes, it is a material item that does not change much over time, such as Jeeps or Chuck Taylor All-Star sneakers—but even these objects change enough that serious aficionados would be able to broadly seriate.
Usually, though, when we are unable to seriate, it is because we are not culturally or socially familiar with the objects in question.
Relative dating methods allow one to determine if an object is earlier than, later than, or contemporary with some other object.
It does not, however, allow one to independently assign an accurate estimation of the age of an object as expressed in years.
They do not, however, give "absolute" dates because they merely provide a statistical probability that a given date falls within a certain range of age expressed in years.