Happiness in the Second Half of Adar

Question

The Gemara tells us that in the same way one must decrease joy in Av, one must increase joy in Adar:

אמר רב יהודה בריה דרב שמואל בר שילת משמיה דרב כשם שמשנכנס אב ממעטין בשמחה כך משנכנס אדר מרבין בשמחה

What about the second half of the month? I think most people assume that the amount of joy is in preparation for the upcoming holiday within that month.

In Av, for example, seemingly after the 15th of Av there is no longer a need to decrease joy. Does one need to continue increasing joy after Purim? Please be sure to provide sources.

Related: Time Parameters of Mishenichnas Adar Marbin B'Simcha

Answer 1

Rashi comments on that Gemara: "days of miracles for the Jewish people: Purim and Pesach". So it seems that Rashi understands that Adar is a time of joy because it begins a period of consecutive holidays commemorating miracles, not because of Purim alone. This may indicate that the joy continues at least throughout the month.

(Though I suppose it could be argued that after Purim there's only one holiday left, which is not sufficient for the extra measure of joy)

Answer 2

The statement of the Gemara is Rav's opinion, which follows his opinion that the mourning of Tisha B'Av applies to the entire month. Thus, according to Rav, just like by Av the mourning applies to the entire month, so too by Adar, the happiness applies to the entire month (See Chasam Sofer (OC 160)).

Note, however, that we do not hold that the mourning applies to the entire month of Av (See Taanit 30a), and that this Gemara is not mentioned in Shulchan Aruch.