The practices of aveilus are in small measure Halacha (Jewish law) and in large measure minhag (custom). Thus, while certain practices are uniform across all Jewish communities, other practices vary from community to community. Oftentimes the customs of one community conflict with those of another. For example, in many communities a mourner does not sit for the entire year of mourning in his regular seat in the synagogue both on weekdays and on Shabbos. In other communities the mourner sits in his regular seat on the Sabbath because not do so is considered a prohibited public demonstration of mourning on the Sabbath.
In my travels from city to city, in the Ashkenazik shuls in which I have davened, I have encountered very few differences in custom – until last night. Last night and again this morning one of the parishioners in Ahavs Shalom in Columbus had yartzhiet for his mother. At the conclusion of maariv and again this morning at the end of shachris, the gabbai announced that the kaddish after aleinu would be recited by this gentleman. Last night I did not understand the announcement and when it was time to recite kaddish after aleinu I began saying “Yisgadal Veyiskadash” only to immediately realize that none of the other mourners were saying kaddish – except for the man who had yartzhiet. I stopped and assumed that there would be no other kaddish for the rest of us to recite. And then after the yartzhiet concluded his kaddish the gabbai began reciting tehilim (Pslams) and the remaining mourners recited a kaddish.
What is interesting is that I have been in that shul on other occasions when there has been a yartzhiet and this custom was not observed. I will have to ask the next time I am there.