I sense the start of a pissing match here and before that happens I would like to know the rationale behind summer repotting. Many (most) species of trees are repotted in early spring because roots are actively growing, I believe, and if/when damage is done to them they are able to push new root growth to recover quickly. How does summer repotting manage that?
I believe the rationale behind summer repotting could stem from the fact that in some climates, trees can enter a period of dormancy during hot and dry conditions, followed by a short period of root growth in preparation for winter. That is the reasoning behind collectors using fall as the second best time to collect Yamadori. The very best time is spring and just before new growth begins. I believe Peter Warren states the obvious very clearly.
"Repot and prune deciduous trees before the buds break and start to grow."
"Repot conifers by late spring, They take a long time to recover, and must be ready for winter."
Published 2014, Consultant Editor William N. Valavanis. Bonsai Techniques Styles Display Ideas.
This advice is consistent with the teaching of professionals i have worked with and studied under. It is common knowledge that an experienced and well trained individual can work successfully outside of the norm with good results.
I believe this applies in particular to repotting, as there are many details that can improve the chances for success both during the process and in the provision of aftercare. Which is why in the right circumstances it make a lot of sense to try an emergency repot. And also why bare rooting can be an excellent skill to have in ones tool box.
From my experience collecting, i have noticed a difference in the recovery period of trees collected in the spring. They appear to do much better than those collected in the late summer, early fall. I collect only conifers. The single most important observation from experience is that the core compact of old soil in the centre is the most important area to deal with. This dead zone creates many issues for Bonsai trees in pots.