That's how I have it programmed and I also use the BCD396XT. I think you're getting confused between trunking and non-trunking (i.e. conventional). Nashua is a P25
trunked system whereas Hudson runs several P25
conventional channels.
For me, I have a system called Nashua that is entered as "P25 Standard (Digital XT)" in Freescan. And for Hudson I created a Conventional system called New Hampshire Conventional. Within that system I have a group called Hudson that has their P25 digital channels stored in it (the image in my last post).
There is one other thing you can do just to make this all extra confusing for you. You can enter any conventional P25 channel as its own system by choosing the "P25 One Freq Trunk (Digital XT)" option in Freescan when creating a new system. That will essentially treat the conventional P25 channel as a single frequency trunking system. That said, I can't think of a reason to do this with the 396XT. I actually do use this type of system with my new SDS100 because setting it up that way will display the unit IDs of the radios. Then if you map out the unit IDs you can assign alpha tags to them. e.g. Unit 10201 = "Engine 4 Officer". I am a bit curious now so I think I'll set up a P25 One Freq on my 396XT and see if it gives me anything extra.
I also just now realized that in Freescan if you deselect "Simple View" you can store the P25 NAC codes. And here I've been search/storing them for years.
If you're still having trouble I can send you my Freescan files for the area so you can play around with them.