Either way one should also use filesystem and file level encryption for sensitive files and encrypt sensitive attributes inside databases. Swap must also be encrypted as it may contain sensitive data. Datacenter bad-drive mishaps do happen as in not shredding the physical drive as a few government and military agencies have recently been embarrassed by.
I do agree with pinkorchid that ultimately drives should be destroyed physically.
This behavior is fundamental; it's what wear leveling is and why it exists. Wear leveling exists to prevent you from writing to the same block repeatedly, which is exactly what you're trying to do with shred.
I'm not sure what other source you're looking for, but I hope you find it. Perhaps, at least, the number of people "on StackExchange, ServerFault and Reddit" and now also HackerNews telling you the same thing is sufficient evidence to stop spreading the idea that shred might work on SSDs. Do what you want on your own systems, of course, but this is dangerously misleading guidance to be offering on an open forum.
So even if wear leveling prevents overwriting a file then such tools should in theory be a risk of data corruption. If this is the case then the tool should be updated to detect if the target is an SSD and abort with a scary message. Perhaps another route is to reach out to the coreutils team.
It won't wipe unrelated files as far as the file system sees it, but it might overwrite some previously discarded internal blocks. "inodes" is a too high-level concept in this context.
You can read more about it on wikipedia which might be an authorative enough source for you? https://en.wikipedia.org/wiki/Wear_leveling
Also note that most ssds actually have more internal blocks available than what they present to the host device so that they can have a "cache" to be able to move things around internally, and also so they can mark certain positions as "bad" when writes to one internal block start failing and still operate properly.