Some time ago, in response to these sorts of stories, I tested several VHF and UHF HT1000s that I had available. EVERY MODEL - AN thru DN, VHF or UHF, worked exactly the same as far as channel steps and wide/narrow deviation (TX & RX). ALL of these radios would do a 5 kHz or 6.25 kHz step (but NONE of them will do a 2.5 kHz step) and all of them reduce deviation and switch in a narrower filter when you select "12.5 kHz channel spacing". Yes, I tested to make sure the radio was really on the frequency programmed..
The ONLY RF performance difference I've noted between the various "letters" is that the DN (and some CN) radios have a 2.5 ppm TCXO in them, and the earlier versions have a 5 ppm TCXO. (stock - yes, you can replace this part with a later version) The controllers in the later models have many enhancements, of course, and since they changed the RF boards, I assume there are enhancements there, too - but nothing that affects whether it will do narrowband or not.
73 DE Hartley