Of course doing this will make the copyright date incorrect in a lot of cases. To change the copyright date you need to change the published work as well. And as I understand it, you should add a year when you make a revision, not replace the year (eg Copyright "1990, 2005 and 2018"). But I'm not a lawyer so what do I know?
Even though you aren't a lawyer, thanks for bringing this up Martin! Made me research and look into it more. Left some thoughts in a different comment based on your comment. Would love to dialogue and come to a better solution.
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