Webbetween the year doma turned gyutaro and daki (also same year he got promoted), and the year of the 113 year ago meeting, another upper moon 6 would've had to have been implimented and killed by the demon slayers.
Webthe last upper moon’s death.
Before slaying the upper 6, gyutaro and daki, it is said that it has been 100 years since the last upper rank demon died.
And in chapter 96, douma.