There is such a thing as believing the integrity of the person you learn from. WSL said he taught the system of YM- I believe him. My teacher says he teaches the system of WSL- I believe him.
GL and WKL have both said that they teach modified systems. I believe them.
I am only speaking for WSL VT. I can't comment on other wing chun.
The point is this in two parts.
1. WSL stated he taught what YM taught him. All of the 1st Gen students of YM say the same and WSL VT according to many around here teaches something fundamemtally different than even YM's own sons. So we need to look at what was also said about YM... that he taught to each student's strengths as a traditional Chinese teacher would. So each will be different in what they teach yet speak truth.
2. So we look at all the various YM systems, including those from WSL, there are differences. Just under WSL, Philipp Bayer is different than David Peterson, both of which are different from Gary Lam and more. Yet all say, to one degree or another, they teach WSL VT. The cycle continues.
It doesn't question integrity, there can be differences...Or we have to say only one student of many speaks truth. This is not believable if one thinks critically because we all bring a bit of ourselves to the Martial Art we study, it only becomes an issue on the degree of divergence which we can not determine for ourselves.
This is why I prefer simply saying the "WC/VT I learned" because all of the systems I have seen 2nd hand and the 2 I have trained, have differences. Thus if the "father" is dead, and thus not here to call out "errors", it's a deconstructive vs a constructive argument. No one here in my opinion can claim "this is what [insertname] taught" if they did not learn from [insertname]. All we can say is that "this is my understanding WC/VT from my teacher", or any art, along with how and when we have used it.
If the above isn't accepted then we would have to say only one person alive has passed on YM WC and he would be a student who never studied under YM. Does that make sense when more than a few who studied directly under YM still live? Because that is how logic works.
So in short, we all know the WC/VT our teacher taught us. That and whether it has served us well is all we can prove. Anything else is a source of deconstruction.