Why you don't want to throw out the bottom of an air-layer

[JoeR]

So it won't work with maples?
This year I air layered my root over rock red maple, at the beginning of September cutted the top which is becoming a raft style maple but the bottom (without a branch or leaves) still alive and will go to the greenhouse this winter in the hope it will bud next year

No it absolutely will work with maples. I was referring to the level of development progress within that time frame. Seiju seem to be magical in my experience in terms of developing rapidly into nice material.