For example, someone who was born on the 1st day of leap August in the 4th year of the Genroku era (1691) would not have had a birthday the following year as there was no leap month in the 5th year of the Genroku era (1692).
例：元禄4年閏8月1日生まれ⇒元禄5年閏8月1日はない。