My guess (and that’s all it is) is that you are connected as the primary user to each service or that the services other than Apple allow secondary users to have the same access as primary users. Apple specifically says on the macOS Internet Accounts panel, where a secondary user would connect to the primary user’s iCloud account, “Only your primary account can use iCloud for Notes, Safari, Photos, Documents, Keychain, or Find My Mac.” However, Apple provides a different mechanism to share Notes, albeit one that requires sharing each note individually. (In iOS 13, a primary user can share a Notes folder with another user, but, in my experience, the other user cannot be running Mojave on a Mac.)
We have come up with a workaround. Recall that this whole exercise was started because we bought a second iPhone, and we were trying to set up Medical ID and specifically Emergency Contacts on two different iPhones for two different users. This second iPhone will almost certainly never be used to access Notes or Calendar or iCloud documents. So, that old iPhone will connect to one Apple ID, and all other devices (including Macintosh computers, where any access to Notes or Calendar or iCloud files will actually be needed) will continue to use the Apple ID that they used to use, regardless of who was logged in. Does anyone see a downside to this? Thanks.