Thank you Senior Robert, since you spent years in both arts, your word means alot here
I have found the similar facts as you. So while the forms of YKS and Ip Man are similar in appearance and its public, for all to see on video, I happen to notice a vast difference in application and energy when they chi sao
In the Yuen Family forms, I see alot of circular fluid movements with various speeds in the forms e.g last part of Sil Lim Tao(perhaps to show white crane lineage). And a great deal of chin na like in Rene's book and Yuen Jo Tong's movements. The Bil Jee shown by Sum Nung student, Master Zhou in guangzhou, also shows different movements and speeds, energy compared to the energy in GM Ip Ching bil jee.
Here for comparison are the 2 families descendants doing bil jee
http://www.youtube.com/watch?v=6Gq0i-13FJcy
http://www.youtube.com/watch?v=ctJ2KMc6VzI
From what I practice and study of the Ip Man family forms, they are not the same in energy.
If Sifu Wong Nim Yi is anyone to reference, the Yi Jee Kim Yeung Dut Ming Dao is not the same as Ip Man Bart Cham Dao, and neither is the lok dim bun gwun taught by GM Ip Ching.
And yes, I can see Yuen Kay San signature in Sifu Mak Yiu Ming Sil Lim Tao, Chum Kil, Bil Jee. Although he does not claim anything back to master yuen, its clear that had a similar source.