The model is built using tags and Group membership. You can completely build up the model from the Items themselves if desired. So you can go in manually to change the tags if needed.
Items must have a unique name. Because equipment is represented by a Group Item, they too must have unique names. So I think your choices are to manually add the Items linked to the Channels that are missing and add those Items to the existing parent Group (as described in the post you lined to in 3) that represents the equipment, or delete all the Items and recreate them all from the Model menu.
To create a feature request to change how this works you should file an issue at the openhab-webui repo. See How to file an Issue for details.