Unriddling the Daisho-reki Calendar

Q.37th year of Tenmei (1787) Daisho-reki [Sugoroku board game]

A mother and her child are playing a game of sugoroku face to face, a peaceful scene with New Year's decorations in the background. Where are the hints to show long months and short months?

7th year of Tenmei (1787) Daisho-reki

Data

Title Creator
7th year of Tenmei (1787) Daisho-reki Trii Kiyonaga
Physical data Subject (NDC)
15 x 10cm 449.81/721.8
Note Call No.
Pasted in "Egoyomi" WA33-1

Answer