Clinto; What would an M923 be called if it had 11.00's on it? Even if it had the A1 designation. Not that I know for sure ,but I've seen trucks for sale under the A1 designation for sale with the duals. I understand and agree with your heads analogy, but for an entire vehicle with multiple different configurations, the comparison to me isn't a fair one to make. What are the differences between the models? IS it just more than the spare tire carrier and the positioning of the bed? There is also a difference in the exhaust mount, not that is a major thing, but yet it is a difference. So for the community ( even new guys like myself that recently found the difference) what should we call them? Just M923?
M939 series, which includes vehicles like your M923 and others like M925, M927, M936, etc. are like this-I'll use your M923:
M923: dualled 11:00s, NHC250.
M923A1: super single tires, NHC250
M923A2: super single tires, 8.3 turbo engine.
Of course there are smaller difference between the various models, but the above is really the important stuff.
If you saw a truck with the A1 designation with duals, then either it's plated wrong, titled wrong or (most likely), the owner sold the singles and converted it to duals.
And yes-there are lots of difference between the M923, M923A1 and M923A2 models. The correct thing to refer to your vehicle as would be M923. This tells readers your truck has the 250 and duals. If you've converted your truck to singles, you still technically have an M923, you've just modified it. If I were asking a technical question and the tires were relevant, I'd still refer to the vehicle as an M923 and tell readers you have converted it to singles.