Charles I used to believe that 15 years ago but I have picked numerous Dissectum seedlings from Beni Shidare since I first moved to my house in 1978 as well as Virdis, they have remained true to form as I have left some of them for some 5-7 years before I pulled them and gave them away, I need to take pics to show you 3 Suminigashi trees trimmed down to less than 3 feet high, these are not from the roots from the mother plant but from established dropped seeds, one of them I cut out 3 years ago, 3 still form a cute little forest and then there is the bizarre big boy at 6 feet high in the cut edged leaf but is green/red. there is no rootstock look a like here nor for the dissectums. I discussed the matter with Vertrees years ago and he said as you but also revertification that indeed some of the best seeds in the best conditions will form true forms.
some years back and interesting development formed and it has been only in 1 year though sadly, due to whatever conditions present 3-4 linear-form thread dissectums popped up but too delicate it seemed to be moved as they all dies when I tried to transplant these little things
I dabbled in root stock transformation with grafts of wax and rubber bands some 15 years ago when we were also budding Cherries in our area.
anything is possible and will happen here in the Platonic sphere, and it's the truth, again I need to take some clear pics so you can understand fully whats happening here on the west side