There is one exception:
$ find . -name '*.hint' -execdir git mv '{}' README.md \;
git statufatal: destination exists, source=1992/albert/albert.hint, destination=1992/albert/README.md
Looking at the two files they differ quite a bit so I've not changed it.
I'll bring this up on GitHub.
We we move 1988-2004 entries from all of a year's winning entries
in a single directory to each winner being in their own sub-directory
under the given year directory.