You are in Ontario, Canada. That means a short summer season. I don't know if you have sufficient growing days of summer to be able to decandle your cork bark pines and have the new growth mature. You would need to decandle about 100 days before first frost, which for your area might be the beginning of June, maybe middle of June. If your new candles have not grown by then, you simply don't have the time to make de-candling work to your benefit. De-candling is the "best method" or "Best Practices" for shortening needles.
You could cut needles to shorten them, but this always leads to brown tips, and immediately gives the impression of amateurism. Best to be avoided.
Developing ramification, treating your cork bark pines more or less as single flush pines is probably the best route available to you.
I always find cork bark Japanese Black Pines to be relatively weak and slow growing. I'm in the Chicago-Milwaukee area, so my climate is largely similar to yours. Cork bark JBP definitely do better in warmer climates. They are not as cold hardy as the normal form of JBP. They are slower growing than normal JBP.
Best styled by "benevolent neglect". Just do some branch selection in late summer or early autumn. Other than that, largely leave them alone.
It looks like you should focus on growing branches, before you worry about needle length. What part of Ontario are you in?
I know of the club, took my father to their show as well. Not alot of JBP.
Have you considered "extension" pruning in the fall? @junmilo
woah. hey.. someone mentioned my name?
We actually do have quite a few black pines in our members collections, but our shows typically have more ewc and maples than jbp's.. I don't know if I posted the photos from the last two shows on here, (if not I will) but there's a pretty sweet shohin jbp that's part of a display.. I've only seen one corkbark jbp at a members house though.
If you're selling any or want more info about the club DM me. Come to a meeting to talk to a couple of our members that have had experience with them if you want some feedback or care info. Our current president is also quite knowledgeable on them. They're all good people.
But, alas we also do have a dreadfully short growing season
Which I'm reminded of when I look out my window between the months of November and May.
Good to see you around here! I am hoping to make it out to your spring show this year!