i) births and deaths
27 July 1925: birth of Harry Towb, whose death last year, three days before his 84th birthday, I commemorated at the weekend.
ii) broadcast / performance anniversary
27 July 2008: broadcast (and performance) of Music of the Spheres in conjunction with Proms concert. I watched this the other week and it is pretty brilliant - wish I had been there for the real thing.
iii) date of real event, implicitly specified in canon
27 July 2012: scheduled launch of the Olympic Games, as seen in Fear Her (2006)