1. Nintendo's figures account for units sold to consumers, not produced total. Regardless of how many sell, Nintendo needs to keep stores stocked.if those numbers are really interpreted as RRRXXXXXXXX Y where Y is part of the unique serial number.. then it would mean 4mil N3DS have been produced. Sales projections for japan at the end of this year are 1.4mil units... I highly doubt they've really shipped 4mil units...
Leaving out that Y part at the end makes the amount of new 3ds pre-9.0 firmware around 400.000, which seems reasonable... looking at the sales numbers, approx 45~460000 units have been sold to date. this is in line with the serials we are seeing (10460000+) however, it would also mean both models would have to share the same range of serial number, since roughly 1/3 of all units sold is a regular n3ds, and there would be no way to get serials this high up otherwise.
2. I think we already knew that about the serial. The last digit is simply a check digit, hence why it's separate from the rest. Around half way through the SNES, Nintendo started using these.
The first unit off the line would have the serial: QJF10000001 6. (Obviously, the letters would vary with the model.)
Edit: And you are probably right about the serials sharing the same range regardless of model.
Edit 2:
Just got my N3DS LL Metallic Blue. It's come with fw 9.1.0-20J.
My friend's relative bought this for me in Japan last weekend. I'm not sure if they bought it at Amazon or at retail store though.
Serial: QJF1039
Wow, thanks a lot for that submission! That greatly narrows down when Nintendo swapped to 9.1.0!
If you look at the spreadsheet now, if you also include the Metallic Black serials, Nintendo started shipping with 9.1.0 in the late QJF10380000's to QJF10390000's.