Questions re 1P Windows (8.4.1)

We still have our wires crossed, but your detailed most recent reply (thank you!) provided the key to unlock the resolution to the issue.

You explained in detail how to edit the tags that are associated with a given 1P item. But this is not what I was trying to do. I want to remove a tag from the list of tags, not to edit whether a given item had that tag. I couldn't figure out any way of deleting or editing the tag itself.

After reading your detailed instructions about editing the tags that are associated with a given item, I thought to myself, "I wonder if the tag will disappear from the list of tags if I remove that tag from all of the items that contain the tag." And that's exactly right. I clicked on a tag in the tag list, then saw all the 1P items that contain that tag, and edited each of those items to delete the assignment of the given tag. When I edited the final item that was tagged with a specific tag and clicked Save, the tag itself disappeared from the list of tags. Eureka!