I've had occassion to study Ken Tai Ichi no Kata which is a part of De Jong's grading system. The following demonstration was posted on YouTube and the participants are students of Hans de Jong, the son of Jan de Jong.
There is also a demonstration that has been posted of the original Ken Tai Ichi no Kata by Mochizuki's school.
The core of all learning is the identification of similarities and differences. There is much to learn from the comparision of the two kata. One of the things that came out of my exploration is the identification of Jan de Jong's bastard child.
This kata and much else is taken directly from Mochizuki's Yoseikan Budo, however, De Jong until 1999 and all of the offshoot schools still identify with Tsutsumi Hozan ryu. In the 1950s, De Jong only had the first four kyu gradings in his grading system. If there is any Tsutsumi Hozan ryu influence in the jujutsu taught by De Jong it would be contained in those grades. Thereafter, his grading system was significantly influenced by his time with Minoru Mochizuki in Japan and through his involvement with one of his instructors, Yoshiaki Unno, who he sponsored to come to Australia and who he and his son trained with each morning for a few years.
What style of jujutsu did De Jong teach and by extension what style of jujutsu do the schools that succeeded him teach?
Even if a case could be made that De Jong learnt Tsutsumi Hozan ryu jujutsu by his original instructors, the Saito brothers, that tradition has long since been changed beyond recognition by the influence of Mochizuki's teachings. However, technically you cannot say they are teaching Yoseikan Budo because De Jong was never graded in Yoseikan Budo. The jujutsu that De Jong taught and that all his instructors teach is the bastard child of the different influences that shaped the school of Jan de Jong.
In 1999, De Jong graded Sensei Peter Clarke (now of Southern Cross Bujutsu)fourth dan and the certificate referred for the first time to 'Jan de Jong Jujutsu.' It is interesting that while everyone identifies with Tsutsumi Hozan ryu jujutsu, not one of De Jong's certificates awarded to students refers to that system. Instead, they all refer to Tsutsumi ryu, an entirely different school. The reference by De Jong to his self-named style of jujutsu was the result of my campaign over many years, however, the four main instructors who have succeeded De Jong refuse to identify with Jan de Jong Jujutsu.
The identification with Tsutsumi Hozan ryu does a grave disservice to De Jong's life work. His legacy is kaizen. Kaizen is a Japanese word written with two characters meaning ‘to change’ and ‘for the better’ and has come to mean ‘continuous improvement’ in business circles.
De Jong continually tried to improve his knowledge and his jujutsu system. He didn't collect books for the sake of them. They were his professional development in an age and environment when professional development through personal contact was not available to him. In his fifties he ventured over to Japan to continue his professional develepmont with Mochizuki and even further by sponsoring one of his instructors, Unno, to come to Australia so he could learn from him.
All the schools that were derived from De Jong's - Jan de Jong's Martial Arts and Fitness, Southern Cross Bujutsu, Indian Ocean Dojo, and Hans de Jong Self Defence School - all continue to identify with the legend/myth that is the Tsutsumi Hozan ryu origins. Jan de Jong worked his entire life right up until his passing developing a body of work and rather than some spurious link to the past, his efforts should be acknowledged and celebrated.
I am proud to say that I teach the bastard child that is Jan de Jong jujutsu.