Earlier quoted context omitted.
It seems as though asimov agrees with you in the last paragraph: >Naturally, the theories we now have might be considered wrong in the simplistic sense of my English Lit correspondent, but in a much truer and subtler sense, they need only be considered incomplete.
That seems false as applied to most of my examples. If the Big Bang theory turns out to be true, then that doesn't mean that steady state theories were "incomplete", it just means that they were wrong. Similarly, if it turns out that eating lots of fat doesn't make you fat, that doesn't mean that previous dietary advice was merely "incomplete".
They still seem incomplete (and not "wrong" to me). They served their purpose and were good approximations for calculations we did and observations we had all those years.
>Similarly, if it turns out that eating lots of fat doesn't make you fat, that doesn't mean that previous dietary advice was merely "incomplete".
Only if "previous dietary advice" was only all about fat, and only if it consisted of just saying "fat makes you fat".