As time goes on, and more and more books are printed
with their LC
numbers, that code would end up coming out as even better.
Isn't it true that every book in the Library of Congress, i.e. pretty
much every book in the English language, has an LC number, even if it
isn't printed inside the book? If so, then LC numbers are close to
ideal book identifiers.
However, an ISBN -> {all equivalent ISBNs} converter would also be
really nice. Personally, I think there's nothing wrong with the
traditional method of identifying a book by title and author though.
Spelling differences can always be solved by appeal to authority: use
the spelling of the Library of Congress.
Axel