Some haggados print sefiras haomer for the second night (outside Israel) at some point in Nirtzah, for people who didn't already count during Maariv. I've seen it after חסל סדור פסח, after אדיר הוא, and in many haggados not at all. I may have also seen it after ואמרתם זבח פסח but I'm not 100% sure.
Is there a reason why printers chose those particular places?
There are those who specifically do not count the sefirah until the conclusion of the Seder. Effort is made to treat the second day of Yom Tov of golus as if Yom Tov is starting for the first time. It is given the same respect, as though there were an actual doubt when Yom Tov begins. Since counting sefirah must start on the night following the first day of Yom Tov, counting sefirah before the Seder contradicts the idea of starting the Seder anew. Therefore, counting sefirah is placed toward the end of the haggadah, when the mitzvos of the night have concluded. Those who count sefirah earlier maintain, zerizim makdimim l’mitzvos, i.e., mitzvos should be performed at the first opportunity. This is especially so regarding sefirah, according to the opinion it is med’Oraisa (a Torah obligation) even when there is no Omer offering.
