Hi Mike,
I think this will depend on how you are using OpenDocument.
If you are opening in the same browser session, then my understanding is that only one user session should be created. If you are using separate windows, then this can increase the user count.
Ultimately, the sessions should time out. An option could be to use a serializes session (serSes), but you would need to use the platform SDK (not REST) to get this value.