I'm not flying NG (or any 737 either) and haven't seen the Chirp, but it seems to me that new S mode is expansion of old one (which is expansion of C) and central to it is 4 digit code (aka squawk) and QNE level. New S mode will have some aditional features like transmitting selected altitude (great fun for any controller with 10+ yr old ATR on her/his radarscope) but I didn't read anywhere that indicated altitude will be also included in transmitted data. Nor I can imagine of what use will that be to ATC, so either I'm missing something or there is indeed a slight mistake in NG manual.