How can I tell if a client is using Windows 8.1 or 8.1 Update.

you could also go to the metro interface and if you see a search icon to the right of your username, the update is installed

Windows 8.1 is a different operating system to Windows 8. The method above or Computer -> Properties will tell you between the two.

"Update 1" was nothing significant and was just a run of the mill Windows update. If the machine is even modestly up to date, you have "Update 1"

How would one determine if the machine is [even] modestly up to date, John?

How would one determine if the machine is [even] modestly up to date  <-- Updates are usually ON and so just run Windows Update and take a look.

Update 1 is not identified except it has a KB number that you would have to look up.

Thanks, John, for the lightening response. :-)

Updates are usually ON and so just run Windows Update and take a look. ~John

Perfect.  Thank you very much.

The selected answer is wrong. If you ask winver, 8.1 and 8.1 update both share the same build 9600.
Rindi's https://www.experts-exchange.com/questions/28443945/How-to-identify-different-versions-of-Windows-8.html?anchorAnswerId=40097880#a40097880 is the correct answer.

McKnife,

Thanks very much for taking the trouble to answer, after the question was closed.  It has helped me a lot.

crb1609