Tsuki-okure (holding events one month later) and the Tenpo calendar are often confused and events performed in tsuki-okure are often called 'old ___' (such as Old bon), and while dates under both systems are very close, they are not the same.
なお、月遅れと天保暦は混同されやすく、月遅れで行われる行事のことを「旧○○」（旧盆など）と呼ぶことも多いが、月遅れと天保暦の日時は近似であるが同一日ではない。