Related על מגילה 1:4

If they read the megillah in Adar I and the year was intercalated, they must read it in Adar II because all the mitzvot that are performed in Adar II are performed in Adar I. R' Akiva said in the name of R' Yose in the name of R' Zecharya ben Hakatzav "They need not read it in Adar II because all the mitzvot that are performed in Adar II are not performed in Adar I except for [the restrictions on] eulogy and fasting that are performed in both." Contracts in each month: In [Adar] I, we write "Adar" and in Adar II, it is written "Tinyan [Two]".