There are many instances of full sentences (even paragraphs) that are problematic as well as single phrases like "superior seed" which really is not "superior" because it is the seed that is less than the "male" or "elect seed." The word is diapherontos which means "different from, at odds with" and "eminent." So "eminent seed" would be a good translation, referring to the lesser female (but still worthy) spiritual seed given to all members of the Christian Church, while the "elect seed" is the more perfect male spiritual seed given to Valentinian Christians.
I think that part of the problem with Casey's English translation, is that the Valentinian tradition was not (and still isn't) understood very well. So it makes the translation process difficult at best.