Correct. I thought your earlier statement regarding junior party was the first to use, but not register, is actually the senior party in its geographic location, thus being the hole in another registrants protection. Correct or not corrrect with regards to what others call "swiss cheese?"
I've never heard the "swiss cheese" nomenclature, but you are correct that a senior user who predates registration can keep a subsequent registrant out of the senior party's geographic area, creating a "hole" in the registrant's geographic reach. I suppose with enough such "holes", the a map of the geographic coverage of the registrant's rights might begin to look like swiss cheese. It wouldn't taste as good, though.