Hi Rich,
By default, Extreme Management Center only collects a subset of traps for historical statistics.
If you go to Reports>custom reports and browse through the target and statistic options, you will see what is available. If one of those statistics is listed, but does not graph any data, then either statistic collection is not enabled or that particular statistic is not being collected for the selected target.
You can verify what statistics are being collected for a specific target by going to administration>Historical statistics collector>statistics collection target. Search for the target and use the show details button. This sometimes takes a minute to load and will show you the traps that are currently being collected for that target.
You could for example see a specific clients Total Bandwidth by going to the Report tab >custom report>target=wireless-client>statistic=client total bandwidth