The heyday of scavenging for lost Doctor Who episodes was probably the early eighties, when the first tendrils of Doctor Who fandom began sprouting in earnest in the US, beginning a worldwide boom-let of popularity that in turn spurred a renaissance of interest in Doctor Who history.
By the mid-eighties PBS stations in particular were hungry for any Doctor Who that was being made or could be found and sold into the system. This worked it’s way both forward and backward from Tom Baker to Jon Pertwee (a combined package of whole colour stories and black and white NTSC copies that were good enough) and eventually to William Hartnell and Patrick Troughton. And of course therein laid a problem, particularly for Troughton for which only five complete stories existed.
For the fervent Doctor Who historians the number 108 is more than a relatively perfect number (2x2x3x3x3), it was the number of episodes missing from the BBC Archives. Rumors were run down in Africa, New Zealand, and Australia. When discoveries of lost episodes were made, such as a complete The Tomb of the Cybermen, it was a cause for celebration.
Christmas came early today my friends.