We have many users with no TZ info. Is there a way to determine who does not use the calendar (i.e it's empty)?

Q: We have many users with no TZ info. Is there a way to determine who does not use the calendar (i.e it's empty)? If not, is it best to add them to the input files and perform updates with our best guess TZ, or better to have user run Outlook TZmove?
A: In this scenario it's probably best to have the user run the Outlook TZmove.