Excuse the rambling nature of this post but
1 - to answer the question, was there 2 412003's ??.
Answer: Gross oversimplification, but what the heck

Yes, some, maybe most, but not all italian racing cars where numbered and taxed for export, for instance most cars sent to le mans, grand prix cars sent overseas etc. Now when you built a new one, why not just affix a number already taxed so you dont have to pay again

, so you can also renumber the old car and sell as a new one, and kind of make money twice. One could argue that their were only one car but why would you change such items as the door screws or headlight fittings, you wouldnt. So when you see the 412003 that raced in 1935 and the car that raced in 1936 you see ahh two different cars. The 1935 car was renumber/ rebodied and sold as new, ha ha. And so................, the same thing happened with 250F Maserati's and other vehicles even Porsche 917's had the same treatment. And at the time who cared ??
2 - I dont have the 8C2900 book, when it came out I was 18 and on a low income and thought, old alfa's ahh who cares, and I have kicked myself ever since. Two or three years ago, I bought the 8C2300 book and my god that is stunning, both presentation and information are stunning. As and when the new 8C2900 book comes out, I will be buying mine. Further what I like is his writing style, far too many authors state things as facts when most things are shades of grey. For instance who knows if something still contains all of its chassis or if it was replaced in its restoration in 1967 or whatever the situation, and Simon has respect for his readers and thus puts the information in the readers hands and then we can make the decision. Unlike other authors who just tell us fake, real, fake, real yadda yadda
3 - need to be careful that we dont give too much information that might be copyrighted
Timmmmmy