You may have several forms or lists using dropdown menus across your site that you would have to update if, say, an individual resigned, or a department changed its name, or a building relocated. Manage this type of information (individuals, departments, buildings, etc. frequently used in lists and forms) in separate lists that we’ll then use to create site-wide lookup columns to replace the many individual dropdowns across our sites that are repetitious. Basically, we’ll update the information in one place and know that it’s updated everywhere it’s needed across our site (or site collection if you’re familiar enough to go the extra mile with collection content types or Microsoft Flow, if your permissions aren’t at the site collection level).
It’s not easy to show a list (or part of a list) from one site collection on another. There are data view web parts you could try in SharePoint Designer, content search queries and page viewers in SharePoint web parts and then some scripting methods you could try, but I, in my enterprise environment, had no luck with those. This method, however, utilizes Microsoft Flow and works flawlessly. Here are a couple great features:
Permissions are completely flexible. Set the “new” list to view only or whatever permissions you like while keeping tight control over the original. People will not be able to access the original list or site collection but they’ll see your up-to-date info you’re wanting to share.
You can set this up so it’s a one-way publishing experience so updates on list 1 show on list 2, but updates on list 2 don’t show on list 1 OR you can set it up two-way so each list will update the other, creating a shared list experience without allowing permissions to access each other’s site collections