How do I ensure that all necessary obb main files and expansions have been downloaded?

I have a game that I'm uploading to the Google Play store. It works fine when downloading manually and runs as expected. However, we are testing on some devices which do not automatically download the OBBs. For this, we had to use the "Google Play Obb Downloader", available on the Unity Store

This ALSO works as expected. However, it's not clear to me how can I check to make sure everything is up to date once the obb has been downloaded.

The DownloadObbExample performs as expected. But once the obb is downloaded, how do I check that everything has been downloaded and the game is now ready to be loaded?

Do I use a WWW call?

I imagine that I'll need to use System.IO and a call like the following

 string path = [The Path where the Obb is];
 if(File.Exists(path))
 {
        Application.LoadLevel("TitleScreen");
 }

But how can I be sure that the file at the path is the completed Obb and that all expansions have also downloaded as expected?