Hi Marco,
You're English is fine, no worries. If I think I might misunderstand, I will ask.
The first 1000 pieces not having a leading alpha letter was something several AP old timers told me (old timers as in long time AP employees) but I myself have yet to see one in the metal as well.
The information about your specific watch is a little questionable given some other "facts" but certainly not impossible. I'll defer to AP's comments on it, of course.
A and B series numbers - I don't have any reason to question mid-thousand serial numbers for A and B series, I've seen some myself.
Differences between A, B, C series -
Not all A series bracelets were market GF; I have seen several which are still with their first owners which do not.
I've seen the "double bricks" (if I'm understanding this term correctly) on early bracelets which were not market GF.
Flip lock - interesting point, I don't remember and would have to check my own personal archives on this.
Crown - I've seen both, but alas, it is quite possible pieces today, even if always serviced by AP, might have had the crown changed as part of the routine servicing, at some point, even if they are in the possession of the original owner. It would be interesting to see what the AP archives say on this; I suspect it might not be 100% consistent even within a letter series.
Thanks for your comments, Marco, it is always interesting to compare notes.
Cheers,
TM