in lib/gitlab/feature_flag_alert/milestone.rb [19:27]
def ago(num_milestones)
major, minor = value.split(".").map(&:to_i)
older_major = minor >= num_milestones ? major : major - 1
older_minor = (0..12).to_a[minor - num_milestones]
self.class.new([older_major, older_minor].join("."))
end