Resolving to aggregate
I’ve spent the last three hours trying to work out a coherent and functional and (relatively) simple set of merger rules that handle all the cases. Ooof. I don’t think I’m there yet but at least it is closer.
So far I’m tending strongly to resolving the case where the new minor is already connected by track from one or more companies, by a) merging the other companies first (active player picks which is the parent), b) selling a share in that merged product, and then finally c) issuing a special dividend for the merged company before starting yet another minor. As is typical in such cases the concept is far simpler than the language.
BTW: There’s a similar mess in Stephenson’s Rocket when a train line manages to merge into multiple other lines all at the same time. There it is complicated by the share trade-up rules, but at least they don’t also have Special Dividends.