- RadioTimes.com
- It turns out Matt Smith was not the first Doctor with a penchant for hats.
Well, this is interesting!
Every year, the British Film Institute holds a “Lost and Presumed Wiped” event. It highlights the fact that, in the 1970s, the BBC exercised a  policy of recording over their own archives after a certain period of time—they would lose the right to air them, or they would assume no one would want to rewatch them, or they would just need extra tapes, but for whatever reason, the Powers That Be figured no one would want to watch decade old episodes of Doctor Who, and they would wipe the originals.
Of the 253 episodes of Doctor Who broadcast between 1963 and 1969, 108 are missing from the archives and thought to have been wiped. (I just linked to Doctor Who's lost episode Wikipedia article, but the entire parent article about the practice of archive wiping worldwide is pretty interesting, if that's your sort of thing.) Patrick Troughton's run as the Second Doctor was hit the hardest by the wipings, and only low quality, silent clips of the Doctor's first regeneration (changing the character from William Hartwell's First Doctor to Troughton's Second) have been located at this time. (It should be noted that audio recordings of all the lost episodes exists, but only thanks to the enthusiasm of the show's geeky fans at the time.)
So! 108 episodes lost, with only two full episodes located in the time since the '90s. And then, Who fans woke up this week and there were two more.