The problem is specific to the iPad app only. The workbooks are still displayed in the web version.
We're having serious problems with this. Until it's resolved, we'll move everyone back to using browsers.
We can ask users to hit the refresh tool in the app, but we can't seriously expect them to uninstall and reinstall every time something is published.
It's too bad. Company leaders love apps on iPads.
UPDATE: Additional details, per Adam's related note: Re: iPad app not showing all workbooks-Reinstall fixes only temporarily
Lots of bugs experienced with the 8.1 app; I have had to restart the app over and over in order to view workbooks.