600A or 600D

How are the two identities differentiated?

I'm not sure. Are you meaning later model with O/2 sensor? If so look at pipe before muffler you will see a sensor there. If nothing there early model. 2007 or so didn't have O/2 sensor. Some had ABS.
ABS will have a small ring mounted to the wheel near axle center.

That is a good question. I have looked at the 2009 and 2010 manuals (2010 Manual) and they mention a 600 and 600A, but no mention of the 600D. Yet, there is a 600D designation.

I've got ABS for sure. About to order front cover and cheap cycle parts is asking which model it is. Thanks for the response. Oh, and y'all can call me Beckers

The A designation is for ABS brakes and the D designation is for non-ABS. The 600 is the same as the D model. The O2 sensor came out in some models ending the 2007 year. All models from 2008 and on came with the O2 sensor. The sensor tells the ECM what is happening with the exhaust gases. The ECM will adjust the fuel/air mixture. Some say that you get better MPG with he O2 sensor. I have not noticed much difference between my 2002 and 2013 Swing.

Great info, thanks

Most people over the years have stated better mileage with the O2 models on. Perhaps driving style enters in? No idea.

O2 models = better fuel management = leaner running engine = better mileage most likely.