Non-web sources for artbooks, doujins and similar stuff

Why is it considered okay to just list the name of the artbook or the doujin in the source field when uploading the scans or digital versions of those, like in post #8225255? The source field is meant to tell us where the file came from, so I'd expect to see "My own scans" if the uploader scanned something themselves, in similar fashion to how you're supposed to write "Extracted from the game" when uploading game CGs that you extracted yourself, or the link to the e-h gallery or yande.re posts that they got it from. Just listing the name of the artbook or whatever in the source field is completely unhelpful to the user for the purpose of determining the real source.

I personally think it's OK as long as they're not uploading obvious samples or brutally artifacted pinterest garbage. Not everything has an active online source, people keep personal archives (myself included) and can't be bothered to cross-reference every upload with the EH/yandere/minitokyo post they got it from years ago. Vintage stuff like the post you linked might not even have a high-res scan available. It's one of those aspects that could be micromanaged but I don't believe it's really productive to do so.

How do you check if something's a sample if the post doesn't point to a source to verify it from? I don't believe old personal archives and/or inactive links make up majority of these non-web artbook and such posts as I see fairly recently released products uploaded a fair amount, and we usually still try to the best of our ability to list the original sources even for deleted artist works, so I don't see why this type of content should be treated as the exception. The source is arguably the most important information in a post and these sources that are just the title of an artbook and such might are as good as completely blanked out sources.