If this is such a serious problem, please demonstrate at least one example in Google Books where a scan shows the wrong letter or number.

That really can’t be hard to do, since there are lots of common books in GB, there are even OCRs available so you could even do the error checking automatically for thousands of books.

If you can’t show a single case of JBIG data corruption in GOogle Books, you have absolutely no justification in calling it such a serious problem!