Ah, badly-written guideline. What it doesn't spell out is that there's
ambiguity ONLY when words are hyphenated at the end of a line. I can see how someone would misread that guideline and add asterisks before every dang hyphen. The more so if the proofer weren't familiar with 18th and 19th century spellings and lacked any sense of how spellings might have changed.
I have been proofing for nearly seven years now, so I suppose some things seem clear to me that might be opaque to a less-experienced proofer.
You're also assuming that the proofer is doing only one page at a time. Many of us P3ers tend to do many pages in the same book, so begin to have some sense of what spellings the author uses.
It might make sense for the project comments to include a list of words that the au hyphenates that might be problematic. A note to the effect that au uses to-day and to-morrow might alleviate some anxiety and asterisks.
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Yup. Or you could say that all the hyphenated words have already been checked once, they will all be checked again in post-processing, and it doesn't matter. :)