Why did the Japanese nishiki-e calendar painters have to disguise the symbols for months in their works?

Question

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The government held a monopoly on calendar printing and only authorized certain printers to produce calendars. These printers were restricted to using a set of approved symbols for the months, with the goal of preventing counterfeiting and ensuring the accuracy of the calendar. However, nishiki-e painters wanted to depict their own unique and creative designs for the calendar, so they had to disguise the symbols for the months in their works to avoid getting in trouble with the government.

Why Did the Japanese Nishiki-E Calendar Painters Have to Disguise