Well stated and thank you for elaborating on some of the same points I have been trying to stress. At the end of the day it's all about your Kung Fu and not trying to decorate your family tree like it's Christmas.Probably a good thing to keep in mind here is the old saying "follow the money". What I mean is, to think about 1) what it is people are claiming, and 2) in that context, that they are gaining from such associations, be it money, prestige, power etc.
So all these people in Guangdong (and or elsewhere) who are running big wing chun schools, what do they gain by deciding they learned from, say, Yip Man, instead of me for instance (a somewhat ridiculous example, but it should convey my point), or Yuen Kay San instead of someone further down in that lineage.... like me for instance (I do know both systems, it could happen [there should be a facetious font]). Its not like people have never tried to jump up a level or two, or three or more in their lineage in order to get above their competitors in the past. And its not like this stuff only happens in the "west" or indeed only in Wing Chun. I know of four who have done it in Yen Kay San style, and that's only the ones I actually know of, I do know that it is happening to a silly level in China, I just don't know the names of all of them.
Then take the Leung Ting stuff from that book he wrote. One of my students has a copy of it and I had a look, I read the Yuen Kay San/Sum Nung section. It reeked of political BS and one-upmanship to me, not to mention irony. I think, (and sorry to any Leung Ting people here, you can say and think what you want it makes no difference to me) that given his somewhat questionable past and credibility (that is his own wing chun history let alone his musings on someone else's), especially in light of revelations in a recent court case, that that stuff needs to be taken with a rather large grain of salt.
Then there is the Ng Chun So teaching YKS and YCW, this again seems to be political BS and in light of the wing chun represented by people with a known and accepted connection to Ng Chun So and the wing chun in the YKS and YCW lines I personally think this is probably impossible. Indeed wing chun going in the opposite direction from YKS to Yip Man is much more plausible; besides its pretty common knowledge that YKS taught Yip Man sticky hands. I have been lucky enough to learn both, and there is no way I can see that you could learn wing chun like Yip Man style (I am assuming this is kinda what he learned from Ng Chun So, after all YM people accept the connection) and somehow come up with anything like Yuen Kay San wing chun. I could totally see it going in the other direction though. If this offends some YM people, sorry, not my intention, I know and mainly teach YM wing chun, its a beautiful system for a wing chun school in a way that YKS wing chun isn't. But there's no way as far as I can see that YKS wing chun could have been developed from the same stuff as YM wing chun at that close a separation (so in one generation).
Then there's the wing chun weng chun problem. I think its highly likely that they are mixed and often its a matter of what people decided they were doing at the time. For example, and this might surprise some people, did you know that Pan Nam figured what he did was weng chun, not wing chun? I have seen it, my sifu went to Pan Nam before he met Sum Nung and PN gave him a book he wrote. On the cover it says weng chun (in Chinese of course). now however PN descendants are calling it wing chun. So, given that it seems the PN bunch can just decide one day they are doing wing chun instead of weng chun, are what all of us doing wing chun or weng chun? could it be that we are all on a spectrum between two points somewhere?
In the end, as I keep saying, and I agree with Nobodyimportant, its the wing chun that counts (or is it the weng chun????) the kung fu speaks for itself.