The older one has more components on its PCBA, has a 2-digit display, has only one jumper on it (that is connected to only one pin), has a different green LED setup, has a red push-push button on it below the green LED, and came in a cream-colored case. I have a hunch that the 'A' is a revision to the model #. Nowhere is there any sticker or other marking stating the model number. I also had a look under the hood of the one I just bought. I just checked the emulator that I bought in 2012 and the sticker on it reads 'SFR1M44-U100'.