@Chango
Thanks for your help. I got some private explanations from Andreas’ guys in Germany, which totally satisfied my questions.
I’ll go visit Andreas the next time I can manage to find some time in Germany. They seem like a friendly bunch. 
@Rene
It might have been advantagous back then to learn the best you can find from different lineages. Back then (1800s and early 1900s) people actually did use their Wing Chun to defend themselves. So, if you could find someone to show you the good stuff, the better.
However, nowadays, it would be a big mistake to go around mixing and matching all kinds of lineages, since, in my opinion, a lot of the Wing Chun knowledge has been lost and replaced by peoples’ own interpretations of “what it should be” without the time proven testing that has been done in the 1800s. So you end of with a “Hodgepodge” Wing Chun, which might be better than the next person’s “HodgePodge”, but still not much better. Maybe it’s not even Wing Chun anymore.
I personally don’t believe in the “refinement and continuation of the development in Wing Chun”. Wing Chun is in the category of the “dying arts” and knowledge already got lost due to societal changes and teachers dying with their knowledge etc. Whatever people think they are “refining” today or “advancing and developing” are useless laboratory attempts at filling the holes in their Wing Chun knowledge.
The best thing would be to find someone, who, as a result of an unbroken line of transmission, actually did learn Wing Chun more or less completely (complete is interepreted in all kinds of ways nowadays..i’m aware of that) and has the fighting knowledge to have tested his understanding of the methods and then stick with those methods. I think Wing Chun needs to be preserved more than anything to keep its effectiveness as a martial art. Mixing and matching won’t do the job.
For example: If you mix one of the Yip Man varieties with Sum Nung’s Wing Chun, I would almost guarantee you that you will end up with something that will just confuse the hell out of you and is probably worse than the original ingredients of the mix.
However, it is possible to pick up ideas across lineages, but that should only happen, if for some reason, your own Sifu is not giving you the whole picture and you have not understood the methods. I realize that that is more the rule than the exception nowadays…unfortunately.
I realize that finding someone like that is next to impossible for most people nowadays, so the next best thing does become going around and trying to complete one’s knowledge by seeking all kinds of self-proclaimed gurus with the exclusive latest findings in Wing Chun. 
I for one, would stay away from a rooster that has the loudest voice and anyone who claims to have learned and mixed several lineages from questionable sources, mostly FAR removed from anyone with verifiable knowledge, created his own lineage, and is teaching all of those today. Unfortunately, there are quite a few of those today…
Take care,
Mustafa