To bring a source for what all here have referred to, that we commemorate all of Klal Yisrael’s tragedies on Tisha B’av, in Kinah 25 (?? ??? ???? ???), the paytan writes, about the 11th century European tragedies, “??? ??? ?????? ???? ??? ??????”; in other words, we don’t add our own day of public mourning.
See ????? ??? ??”? ?’ ?”? ?”? for an explanation of how this is not contradicted by the fact that certain communities did, in fact, observe days of mourning in commemoration of tragedies which befell them.