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> Perhaps we are looking at different files; 
Indeed, I was looking at the 3.2.0 database (assuming that it would be
the same in subsequent versions).
> ISTM the problem is that implementing the default-to-uppercase was not
> done in Tools/unicode/makeunicodedata.py where full information is
> available. This left no way in _PyUnicode_ToTitlecase of resolving the
> ambiguity of a zero value for ctype->title -- is it "no titlecase
> supplied so use uppercase" or is it "titlecase supplied, delta == 0,
> means ch.title() -> ch"?
Correct. So it seems this needs to be fixed in makeunicodedata.py
already. This was not the case with earlier versions of Unicode (which
never had a mapping to the same code point).
The logic for using deltas is also incorrect, so makeunicodedata.py
needs to be fixed anyway.