I would think that a master that has studied his main art for 40 or 50 years (and probably has experience in other arts as well) has a depth of knowledge that goes beyond what is taught to his students. For one thing, the master decides what to teach. He may decide not to spend time on teaching some things he has learned as he considers them less important/effective, preferring to stress other concepts/techniques. Many karate masters knew more kata than they taught. Another thing is that few students stay with their master long enough to be able learn all the system has to offer.
More important however, is that it's impossible for a master to teach all he has learned. There are things that cannot be taught - they must be learned/discovered by the student himself during his long MA journey.
Yes and yes kind of. Most early first gen direct Yip Man students are gone so all we have for proof are stories that they left behind. The only video evidence is the video of Yip Man doing the first 2 forms and the dummy. What he is doing in that video has many differences with forms performed by his early students and later ones as well.
Yip Man changed or held back things for many reasons. For example , the first person he taught the dummy to in Hong Kong,Yip Bo Ching, used a technique in a fight and seriously hurt some one. Yip Man changed the dummy form by removing that technique,. In an old Interview Hawkins Cheung talks about Yip Man teaching people different things if they were having trouble getting something. I was at a dinner where Yip Ching explained why his knife form was different than Yip Chuns same type of thing.
The only people that really got close to everything were the few private students that paid a lot or the early fighters since Yip Man reviewed fights with them and showed them different solutions when they lost or got hit. This is how the gaan sau got added to the SNT Yip Man taught. It was not in the early form he taught.
Wu Taiji vs Tibetan White Crane