Content published before the two universities existed carries no uni tag, so the split is enforced only in the browser. Stamping every old document lets the security rules enforce it on the server, where students can't bypass it.
Run the scan first. Server-side isolation can only be switched on once nothing is left untagged — otherwise that content would disappear from the site.

👁 = shown on the site  ·  🚫 = hidden (content kept, invisible everywhere)  ·  🗑 = permanent delete (subject + ALL its content). Changes apply after pressing Save Changes.