The yik kam wing chun siu Lin tau instruction note is a teaching of 1850 and before. It goes into in depth and details of internal art practice and description of the root source of the core elements such as power type and Qi development type .
With the snake crane wing chun secret note, we know solidly what happen in pre 1890. With the echo between this note and yik kam wing chun siu Lin tau document . We know they are real deal. Also we can see how yik kam document cover the internal depth of the Wck where snake crane wing chun note left off. And snake crane wing chun note cover the specific application view where the yik kam siu lin tau document didn't cover.
Thus, with this two documents, they verify each other's and show us both the big pictures and details of wing chun kuen from 1850 to 1890. It tells the stories beyond Leung jan into Leung LAN Kwai which is Leung Jan sigung era. Thus, we do have a sight on what is going on and how is the evolution.
We learn from these two notes which is from isolated red boat lineages for past 160 years, the root of Wck is indeed emei 12 zhuang and white crane from fujian. The shao Lin mention in the legend of Wck history is a pseudoname of the Hung Mun in 1850 era not real shaolin temple.
So, if one is looking for the facts on ancient Wck. These two notes have described them. It is a view one can see how the art evolve since 1850 to today, what change , what missing. What get add in. It is this simple.