Haplogroup B-M42 is descended from A2-T about 70,000 years bp, possibly originating in western North Africa or central West Africa. The paragroup or haplogroup without additional lineage definition has not been found in modern populations. It is therefore known by its descendant lineages.
Prior to 2002, there were in academic literature at least seven naming systems for the Y-Chromosome Phylogenetic tree. This led to considerable confusion. In 2002, the major research groups came together and formed the Y-Chromosome Consortium (YCC). They published a joint paper that created a single new tree that all agreed to use. Later, a group of citizen scientists with an interest in population genetics and genetic genealogy formed a working group to create an amateur tree aiming at being above all timely. The table below brings together all of these works at the point of the landmark 2002 YCC Tree. This allows a researcher reviewing older published literature to quickly move between nomenclatures.
^van Oven M, Van Geystelen A, Kayser M, Decorte R, Larmuseau HD (2013). "Seeing the wood for the trees: a minimal reference phylogeny for the human Y chromosome". Human Mutation. doi:10.1002/humu.22468. PMID24166809.