Apple states that the upgrade process affects the reminders in your primary iCloud account only. Reminders in all other accounts, including secondary iCloud accounts on your device, remain unchanged.
So just to clarify, we have an older Kitchen laptop running High Sierra with certain Reminders like Grocery List. All our personal computers have in addition to their primary iCloud account a secondary iCloud account of this older Kitchen laptop so we can all see the Grocery List.
If we upgrade the Reminders app on our personal computers, I assume we should still be able to see and sync the Grocery List, according to the Note from Apple. Right?
What about the other way around. If the older Kitchen laptop has as secondary iCloud account one of those upgraded Reminders accounts from our personal computers, can the older High Sierra Reminders app see and sync those upgraded Reminders?