I couldn’t find this in the style guidelines, so forgive me, but depending on if a work uses the word (inch) or the equivalent symbol (″), should each usage be respected and retained, or are there any rules for standardising such cases? For example should inch always be written as the word, as the symbol, or interchangeably depending on how it was used?
I don’t think there’s any guideline for this, so just use what you can find on your source. There is a preference for ″ over " (regardless of the source), but since not a lot of keyboards have the proper symbol for double prime, it’s just a preference, not a rule.
There is a Miscellaneous guideline stating that typographically-correct punctuation (if someone is able to type it) is preferred over basic ASCII punctuation characters.
And indeed the correct character representing inches is ″ DOUBLE PRIME (U+2033).
Thanks @chirlu, I had not understood the question properly!
Note that the Miscellaneous guideline does not say “Use the symbol instead of the word”, though.
I think we generally prefer however it’s written on the release. If the release has both ways listed (e.g., one way on the back and another way inside the booklet), then just pick one and go with it.