@River's Edge do you have any tips for me on developing branching and managing vigor?
First off the tree looks very healthy and in great shape to continue working. This is more than half the battle. When I look through your recent pictures I see considerable density with a distinct lack of direction. Your question is spot on.
Steps that are often missed are the follow up to cut back and dealing with the effects of decandling.
It appears that you are not reducing down to two buds after decandling and perhaps you are keeping all the back buds that occur. It also appears that you have not been practicing any needle reduction in congested areas.
It is not fair for me to suggest what happened , only you will know what steps were taken or missed. One of the main difficulties with advice over the internet is deciding how much detail can be included in a response. Most techniques involve several steps that may or may not be used depending on the circumstances. Developing branch structure is one of those for sure. It also helps if the individual understand that each branch cannot be treated the same when they are developing at different rates.
When you cut back to induce back budding, one should also wire down if needed, and reduce needles in areas buds are not decided or where they may shade out desired existing buds. Buds that are not in desirable location will be removed unless needed for health and keeping the branch going strong until new buds are in the desired positions. When you go back to read the last sentence you will note that choices need to be made each time based on the individual branch.
When you decandle the newly formed buds will be thinned down to two, unless the design calls for less in that position. Usually two of similar strength that are side to side. Those pointing down or up are usually the first to go. This may change if directional change is desired and the position and angle of the buds suit the directional change.
In both cut back and decandling it is important to time the development of interior buds, giving them sufficient time to develop strongly before reducing the branch and building out from the new shoots. Think approximately two to three growing seasons.
Bifurcation occurs from selecting appropriately located new buds and thinning the surrounding areas of extra needles and unwanted buds in order to give them the space and time to develop.
Boon created an excellent series of DVD.s on Black Pine. The one that would benefit you the most at this point in time is entitled " Fall maintenance"
I feel willing even mentioning this but here goes. When I go back through this thread I notice a distinct lack of wire. It appears that you are attempting to style a pine without wire. All new growth will turn up regardless of initial position. It is very difficult to open up the branching to develop new buds without the use of wire. Boon expresses it in this manner.
" Wiring is essential to creating bonsai that reflect your skill and effort. When you wire, you do more than just train a bonsai; you open up the interior to get more light, thereby stimulating new growth."
"Needle pulling, pruning and bud thinning techniques preparing JBP for the new growing season"
When one has new healthy shoots to create branching from, the first thing to be done is to wire out and down opening up and beginning to form pads.
So I would also suggest checking out the Boon DVD " Wiring and Styling: Japanese Black Pine"
Full Caveat, I understand that similar instructional material may be available from many other sources,
Apologies if my comments are too direct. I try to go direct to what I think.