Once the deadline has passed all frequencies will be narrowband (even the old ones that used to be wideband). They've added some new frequencies between the old ones to allow more users on the band, which is why they did the narrowbanding in the first place.
It's kind of like you having an old beat up blue Mustang. You fix it up and paint it red. Is it still a Mustang? Yes, it's just no longer blue, nor is it beat up. You had an old wide-band frequency on UHF. You sent in the paperwork to change that frequency from wide-band to narrow-band and got new radios. It's still the same old frequency, now it's just narrow-band and you'll be able to keep using it after the deadline. The frequency didn't change, only how wide of a signal you used on that frequency changed.
I think where a lot of the confusion comes from is in the distinction between deviation and channel spacing. Deviation being how far away from the carrier the signal normally goes and channel spacing being how far away two different radio signals can be without interfering with each other.