Y-chromosome DNA SNPs (single nucleotide polymorphisms) are not always from anthropological or even historic times. Some Y-chromosome DNA SNPs are restricted to a single family that is related in genealogical times (one to 15 generations). These are family SNPs or private SNPs. Other SNPs are slightly older. They represent paternal lineage groups that predate the adoption of a family surname. These are semi-private SNPs.
Currently, family SNPs and semi-private SNPs are not common.