In the case described above where I open one app from another (either into an iframe or a new tab), it is not necessary to share tables between apps if you want the newly opened app to be completely self-contained.
In my case, my main app acts as a hub to authenticate users and present them with downloadable media or a a link to other apps. It stores the urls for these apps in a data table.
The only table I want to share between apps is the Users table and now this is possible from the solution here:
So all is well now. Thanks Anvilistas.