Laura,
Historically, Legacy Brocade followed a method called "Target Path". While there are new releases all the time, they would recommend to upgrade to a specific code path unless there were features in a newer code that were needed. This is to ensure that the most stable version is recommended to customers in general.
Extreme has continued this recommendation style (it sounds like Ruckus/Arris has done the same). The official documentation for Extreme Network OS is here:
https://documentation.extremenetworks.com/networkos/HW/extreme-nos-target-path.pdf
I can understand that this document is confusing as it lists multiple versions. In my experience I like to see customers running the latest letter patch of NOS 6.0.2. If you are interested in IP Fabrics, then we would recommend to moving onto NOS 7, otherwise it is fine to remain on the NOS 6 release.
Thanks,
Mike Morey
Principal Technical Support Engineer
Michael Morey
Principal Technical Support Engineer
Extreme Networks