Thanks for your swift reply.
Yes, I know a different login is required for each device. But I am talking about the global Apple ID that one uses to access this Apple Community forum as well as iCloud and other things. When I want to log in here, I get this:

If I choose "Continue with Password," I use a previous Apple ID password and I log in. But if I choose "Use a different Apple ID," I get this:

See, it has the same handle, but it does not accept the password I used to login in the first screen; it accepts a more recent password, created a few months ago, and logs me into the same user area. They shouldn't both work! But they do! The same situation obtains when I log into iCloud. Extremely confusing but I can live with it. My primary problem at the moment is that when I add, edit, or delete a contact or reminder on my phone or laptop, I want those changes reflected on my desktop, which currently they aren't nor do they appear in iCloud, although, as I wrote in my OP, the reverse does work; when I add, edit, or delete on the desktop, the changes do appear in iCloud, and my other devices. Makes my head spin!
[Edited by Moderator]