Dating systems are sort of "meta" ways of looking at time measurement. They suggest ways that days, years and decades can be organised into groups that are more associative than mathematical. Perhaps the most obvious example is the BC/AD split, which occurs because of the existence of Jesus Christ, a real historical figure in the DWU (see: Byzantium!) who is significant to time measurement because some believed him a deity.
Equally, the Victorian era is a "dating system" more than single "date" because it deal with that range of time while Victoria was on the throne of the United Kingdom.