Glad to hear of your success.We all have to experiment and in the case of JMs usually with some fatalities along the way.Many people simply can't root prune in autumn as they know in a few short weeks temps. will quickly and dramatically drop to well below freezing.I have a choice temp-wise but do it in autumn because spring is so windy and wet here.Young JMs don't always survive this without my interference so I'm not gonna stress them more.Obviously spring repotting is going to delay their take off anyway but they should catch up eventually,but if they've had a hard time in winter it could tip them over the edge.
On a similar theme I've had to experiment with the best time to do the main pruning of the trees.For me pruning during dormancy is a bad idea.My climate is only briefly cold enough to halt bacterial growth and pruning cuts at this time are often infected and spread unhindered through the plant.I've even had a couple of untouched 6footers knocked out by this,so again I'm not gonna risk it anymore.
We all live and learn and it's certainly disheartening when you lose a nice plant....but it's always an excuse to get something to replace it :)
Wishing you&everyone a continued success this year....spring's not far away YAY!