Thanks Kevin, I hadn't thought about the history of it, even though I've had those different accounts over the years!
I'll go back to the clients and see what exactly they have disabled and ask if they can try different configurations that meet their goal of blocking file upload to iCloud without also blocking sign in. II imagine they just selected every option available to ensure the most restrictions. I looked at the reference you mentioned and see what you mean, not a simple "block iCloud".