Frege to Russell
I'm back.
In the meantime, Marcus Rossberg has kindly looked up the translation of Frege's third letter to Russell that I was talking about recently. He writes:
I checked the reference and the apparently false negation is in there! It's on p. 141 in Gottlob Frege's _Philosophical and Mathematical Correspondence_, ed. by G. Gabriel et al., Oxford: Blackwell 1980:
"But the difficulties here are not the same as in transforming the generality of an identity into an identity of ranges of values."
I guess you're right that the translation is based on the _Wissenschaftlicher Briefwechsel_, Hamburg: Meiner 1976, at least it says "originally published as..." in the front of the English edition.