It is not what I think. It is what YM taught to WSL, and which he passed down to others. I can evaluate different ideas of what YM taught by looking at their coherence and degree of non-contradiction. Some have lots, other have little, others none.
What constitutes as a "contradiction" though? How do you know that there's not a misunderstanding at play on your part of what other people are doing instead of on the part of others for their own system? (Not trying to say you're wrong, I'm just addressing what I see as a bit of a leap of logic)
I can use myself as an example here, in another thread I brought WSL's heel-pivoting mechanic into question, and from the discussion that resulted it turned out that, as an outsider, I was simply looking at it the wrong way. Who's to say that a VT guy can't make the same kind of error?
Plus, let's say that WSL's system is the most coherent and non-contradictory one out there out of all Yip Man systems. What's wrong with crediting WSL's own genius and talent for it? After all, he's one of Yip Man's students that actually went out and fought with Wing Chun. That sounds like a good way to find out what works and what doesn't and adjust your system accordingly.
A good example of this is the Tan Sau-Gan Sau-Tan Sau in section 6 of the form where it used to be Tan Sau-Jum Sau-Tan Sau. It's well known that WSL is the guy that pioneered that change not just in his own WC but in Yip Man WC as a whole after he brought the subject up with Yip Man. Why not say WSL was a smart guy and credit him for it?
Another way of looking at it: If we assume that WSL's system is the best, I think using that as evidence that it's the closest to what Yip Man taught is shakier ground than it is to say that Yip Man's teachings changed over time. You could look at Yip Man's Foshan students and speculate that perhaps taught the same things then as he did when he died and then his students added mainland WC into it later on. The problem with that is that we see a visible pattern in Yip Man's students from the Foshan, early HK and later HK days. Lineages from his Foshan days show a style very similar to other mainland styles, lineages from Leung Sheung and Lok Yiu show forms that are different but still similar mechanics to the mainland styles, with this same idea applying to Chu Sheung Tin, but to a less significant degree. Coincidentally, he started learning after LS and LY did. From WSL onward -- with the exception of Leung Ting who many aren't sure actually learned from YM in the first place -- we see systems that are basically the same as each other in terms of mechanics -- a good amount of them just have crappier instructors as a norm, based on what Sifu Youtube (I stole that from Geezer btw) has been able to tell me, compared to the WSL lineage
I take that as
very credible evidence that Yip Man re-evaluated his teachings over time. It might not be full-on concrete proof, but IMO it stands up to scrutiny better than saying "WSL has the best system, therefore it's the closest to what Yip Man taught".