Don't ask me how I do these things. Somehow I ended up pushing the wrong button(s) in my Movable Type install and completely overwriting my custom template set — which took me something like two years to build — with the default templates.
MT, fortunately, had the good sense to store backup copies of everything. It does not, however, have a pushbutton way to restore those templates to the land of the living. You have to copypasta, as the kids say today. I did so much cutting and pasting I thought the C and V keys on my keyboard were gonna lose their silkscreening.
On the plus side, it gave me the chance to throw out a few template modules that were sitting around doing a great deal of nothing (and potentially inspiring a bit of confusion).