First, let me welcome you on our Patek forum and I hope you'll find the info you'll be looking for 
About your questions, you have very precise ones and I must say I don't know this reference enough to answer it in a reliable way.
The thing is that, in the past, customised watches were more frequent and you can also consider that an earlier owner asked for a change.
I guess that what I would do if I was really wanting to know more about my watch, is that I would start from the official papers (or Extract from the Archives), use those informations and see if they are still coherent with my watch. In a second time, I would ask directly to Patek (I see from your country that you may talk to your Salon as well) and they can tell how they can handle this and make the research for you (if the watch has been serviced at Patek, they can have the track record of the servicing operations).
I think this is the best way to get your answers. However, we have some very knowledgebale members here as well and maybe someone will be able to bring them.
I've been doing the same kind of work for the 3970 and I must say this is the same difficult task, there are the "global" series but you also have all kind of exceptions. And the sources available today are not always 100% reliable.
For instance, I saw in the Patrizzi that a 3940 was sold on July 1989
but it has the n°771 612. Thus produced before 1989 and with a number
out of your 770701-771500 range.
About the production numbers: PP never communicates about them and usually the figures you can find are only rough estimates but nothing official (thus 100% reliable). Maybe that, back in the earlier days, some figures might have leaked though.
Please let us know if you find your answers, we will be interested in knowing.
Until then, enjoy your beautiful watch and do not heistate to share some shots in the future!
Cheers, Mark