You'll see ports listed as 'NP' (not present) for various reasons. The 2 most common are: 1) If the platform you're on supports expansion modules (VIMs) and none are installed, there will be placeholder port numbers listed as NP 2) If the platform you're on supports SummitStack-V (Stacking via normal ethernet ports), and you have stacking-support enabled, relevant ethernet ports will transition to 'NP' as they're no longer available for normal ethernet data connections as they're locked into being used for stacking. This is controlled by the command 'enable/disable stacking-support'. Auto-discovery is related to how a switch finds neighboring slots, but the enable/disable of stacking support itself controls what ports are used for stacking.
You can find a list of stack port numbers here, this may be helpful. https://documentation.extremenetworks.com/exos_30.6/GUID-2409A08C-9642-4245-9DB1-D7893DA1662F.shtml