Although thinking about it some more (now that I have managed to split them)
If I add my noshare label in the sharing section, then the shared user should not see the 4K versions in her continue watching. Is that correct?
(I understand that if I were to watch the show I would see 2 items in continue watching, but I can deal with that.)
Edit
To answer my own question. I tested with another Plex account I have and confirm that only one item appears in continue watching if the 4K Show is excluded from sharing via the sharing label restrictions.
This show has been Split Apart, so Plex sees 2 Shows. The 4K version has a sharing tag applied to exclude it from being shared
I then get a new episode in both 4K and 1080 versions, I put the 4K copy into the folder in the TV4K folder and the 1080p copy goes into the TV folder.
After adding the new episodes and scanning the TV Library The 4K Version of the show has 2 items of the added episode (both the 4K and 1080p copies) and the show in the other āregularā Library does not see the new episode.
The only way to fix it is to split apart the show with the 2 items and then re-merge the lone item with the 1080p version of the show.
And when splitting apart the 4K show it then looses the no share tag that I had previously applied to it.