Rabbi Blumenkrantz A”H, was makpid that there should always be a shalom zachor, and a kiddush for a baby girl. (The kiddush could be made up at a later time or even combined with a kiddush for another simcha.) For those who had not had a shalom zachor at the proper time, he encouraged them to make it up at the next opportunity. For the 9-year old who missed because of the Seder night, his family made a shalom zachor shortly before Pesach (used up some of the chametz).
The 40-year old made his own shalom zachor and had his mother as a guest.