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Has the designer abandoned this sim?No, but AFAIK they secured a government contract towards the end of 2016 that's been keeping them very busy since. If you have any questions it's best to write them directly by email. We should benefit greatly from that contract work eventually, but we'll have to be patient for now...
Over the years I have bought two iterations of the software. I did it to support this innovative sim/game. It was never a complete game. We could play both sides. Some aspects of the sim worked better than others. I always felt my purchases supported a design-in-progress that I wanted to see reach its full potential.You might want to ask that by email, I gather things are a little busy and it may take a while for them to stop by here, especially as quiet as things ahve been here lately...
Will the newest version be made available as an upgrade for prior purchasers?
For multiple plans  to  (numbers can be skipped), file naming you add " ^[nn] " to the file name.So basically you save a plan and add "^xx" to the file name, where xx is the plan number (see screenshot below).
If "default" ( no plan number ) file is found, it is ignored if numbered plan is found. Otherwise, default file is used.
Each plan can have unique groups, group names, and scripting orders...
It is a combined human general, randomness of plan, and AI (as soldier only after general is done!).
This is same and can be used for Non-AI scenario groups.
To make the plans, save a group/scripting in regular scenario, then rename and add plan number to filename. Later save more
plans and give them numbers. Later you can copy them to AI folder.