An object earns its place here by what a tradition does with it, not by how old or valuable it is. A vestment is worn, a ritual item is handled in rite, a symbol is read, a relic is venerated for what it is claimed to be a remainder of. The categories overlap more in practice than the boundary suggests, and an object can be sacred, symbolic and later a relic once its owner is gone, so entries cross link rather than forcing one answer. Where an object belongs to a closed or restricted tradition, the entry describes what it is and what it is used for without reproducing its regalia or restricted symbolism, the same caution held throughout the atlas for material a tradition does not display outside its own initiates.
The overlap is not hypothetical. The Stone of Scone was a ritual item, the enthronement stone of the kings of Scots, until Edward I seized it as spoil in 1296 and built it into the coronation chair at Westminster Abbey, where it kept being used, now in a rite belonging to the tradition that had taken it, the same object doing double duty as a working seat and a venerated token of conquest rather than one giving way to the other. The Black Stone set into the Kaaba shows the same doubling without a change of hands at all, pilgrims kiss or point to it as they circle the Kaaba during the hajj, an object actively used in rite, while tradition simultaneously traces it to Abraham, so it is used and venerated at once rather than in sequence. A relic can also arrive without the object it began as ever surviving to be labeled one: the Second Temple menorah vanished when Rome carried it off in 71 CE, so it never itself became a relic anywhere, and the Arch of Titus's relief of soldiers bearing it away became the enduring symbol read in its place instead.