Upvote:1
I interpret the following quote to mean that there were multiple conflicting signals that would trigger a change to an era name, and that it may not be possible to clearly identify a system.
Prior to the Meiji period, era names were decided by court officials and were subjected to frequent change. A new era name was usually proclaimed within a year or two after the ascension of a new emperor. A new era name was also often designated on the first, fifth and 58th years of the sexagenary cycle, because they were inauspicious years in OnmyΕdΕ. These three years are respectively known as kakurei, kakuun, and kakumei, and collectively known as sankaku. Era names were also changed due to other felicitous events or natural disasters. Wikipedia: Japanese Era Name
Aside: the metaphor that springs to mind is "Xnomics" when an elected official needs to shore up support or market for some initiative, they assign a catchy name and build stories around it. Activity that if it were carried out in the internet would be called "memage". I suspect that pre-Meiji era names were "memage".