@MarjaE - I find editing file names in my file manager easier than editing columns in calibre, especially if it involves cutting and pasting from elsewhere. As you suggest this is common for journal articles, blog clips, non-ebook files, etc.
So, when I want to add books that have missing (or incorrect) embedded author(s) and/or titles, I ensure Preferences->Add Books->Read metadata from file contents rather than file name setting is unchecked.
I should add, I use Windows, and more importantly several 3rd party utilities that facilitate this approach.
BR
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