The popular belief itself is certainly encyclopaedia-like content regardless of its truth. For example we are quite sure now that Hera or Zeus are only myths but they have their place in an encyclopaedia. I think speaking about national catastophes we need only those that were really fatal blows not everything that went wrong in the course of our history. I think the traditional list is quite obvious: 1241, 1526, 1849, 1920, 1956. Luckily no present-day event has a similar magnitude, from some wider perspective they are only a strong storm, small riots etc. What the article really needs, I think, are literary sources mentioning the curse. I vaguely remember for example a Vörösmarty poem from the 1850s but I'm not sure.