This is going back a bit but I've been looking at all of the old posts trying to gather information on the SM's to help with my search and help me narrow down what I actually want. From what I've been able to tell Bill, the Amel 12 Letter serial number system for the Super Maramu's works like this:
First three letters are the company (AML)
Letters 4&5 are the Model (SM for Super Maramu)
Letters 6,7 & 8 are the Hull Number (387 in your case)
Letter 9 is the Month as you say (where A=January, B=February.... L=December)
Letter 10 is the last digit of the year it was built (in your case 2002)
and then the last two letters (are the model year - in your case 2003)
I've looked at dozens of SM's and they all fit that pattern excepting two very early ones (a 1992 and a 1990 Annie) where the patterns make no sense at all (and aren't 12 digits) which make me think that there might be a transcription error like the HIN above in this post which doesn't make sense either as you suggest. Those boats are early enough that it is possible they didn't use this scheme (I don't have an earlier data point that would suggest they didn't) but in 2001, the scheme you pointed out was definitely in effect.
I've also noticed that the point the model year jumps ahead of the build year is somewhere between April and September (with September being the most prevalent but a few examples of July/April thrown in to confuse things). Anyway, the more I dig, the more I discover that they are all great boats (with a few notorious examples) and it's just a bit of trivia that maybe Olivier can explain to us.
Future Super Maramu Owner