Let’s try to go through this methodically,
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According to most accounts there was a Leung Bik. In a one account, there was not, and in another, he didn’t end up in HK, but in the common Yip Man lineage account, there was and he did. This then becomes a “we don’t know”
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The answer to the first part of this question, based on everything available to date, is “probably no”. Given that there are other lineages from the Red Junk, and from Wong Wah-Bo, and these broadly match what Chan Wah-Shun taught, it is “very unlikely” anyone other than the common originating source (Red Junks) could have formed it. As to whether or not Leung Jan’s sons learned different WCK, or any WCK, this again varies into a “we don’t know” but based on the same common available information, it seems “more likely” they learned the same WCK as everyone else.
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Since accounts on this vary within the Yip Man family (many saying yes, a few saying no) it is another “we don’t know”. Evidence seems split fairly evenly down the middle, making it impossible to determine likelihood, IMHO, and lacking any third party coroboration (ie. lineages from Leung Bik not through Yip Man) that’s all we’re left with.
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As above “very unlikely” although we can’t rule out the possibility Leung Bik might have either learned or created another version of WCK after leaving Foshan, and taught that to Yip Man (the culture of face causing him to attribute it to his father regardless of its real source).
On the Yip Ching derived story, if its true Yip Man only learned up to Chum Kiu from Chan Wah-Shun and Ng Jung-So (possible, as Ng seemed notoriously stingy with teaching material), and learned the Biu Jee and the rest from Leung Bik, it makes it “very unlikely” Leung Bik taught him anything other than typical Foshan WCK since the Biu Jee Yip Man taught his HK students, including Leung Sheung, Lok Yiu, etc. is very, very close to the Biu Jee from the Fok Bo-Chuen/Yuen Kay-San lineage. Had Leung Bik taught anything else, the only Biu Jee Yip Man could have passed on would have been closer to William Cheung’s.
As to the different education/comprehension levels of CWS vs. LB, this part has never made much sense, unless CWS was completely illiterate or daft. WCK theory is not particle mechanics, most have us have read the Kuen Kuit and been taught the theory, most of us have kung fu uncles that range from tradesmen to college educated, do we see this reflected today? I have sibaksuk who were butchers and ironworkers, and sibaksuk who were engineers or university grads, and they all have the same basic knowledge.
Besides, in the story, Yip Man was still young, and only beginning his education, would the education level of his sifu vs. sibak make that big a difference at that point in his life?
WRT the TWC story,not only did CHan Wah-Shun never notice the Leung family doing anything different, he somehow failed to notice that what he was learning was very different from what he had been “peeking” at through the fence.
WRT the other lineages, Chu Chong-Man is part of the Weng Chun handed down by Wai Yan to Andreas Hoffmann, and Pan Nam is in large part Leung Jan derived (via Chan Yiu-Min/Jiu Chao and Lai Hip-Chi). In parallel, we have Fok Bo-Chuen/Yuen Kay-San, and the Cho family, none of which have any connection to Leung Jan, but are very similar in core, and Koo Lo, which decends from Leung Jan’s later teachings.
Since, as mentioned, these are remarkably similar in core to Yip Man WCK, it seems “unlikely in the extreme” that Leung Jan could have “modified” anything into them. He may have learned something additional that was different (another system/branch), or created something, but it looks fairly certain what is now practiced as Sum Nung, Yip Man, Koo Lo, Cho, etc. are what WCK was from the Red Junks.
So, while its possible Leung Jan, Leung Bik, Yip Man, or William Cheung either learned a divergent branch or different system, or came up with a different system, the standard story of Yip Man’s WCK being “modified” from something else is unsupportable.