We really need complete forum index/tree so we can access subforums much more easily.
I have precisely the thing. A map of *all* of Stardock's forums on *all* of Stardock's sites that can access these forums.
However if you're looking for clarity this may not be what you want. I currently list 775 forums spread over 11 sites of which 373 forums are unique. I do intend to publish the raw list of forums but I am in the process of trying to correlate which forums are shared among which sites as well as trying to find a way to present this massive amount of data in a logical format.
In the meantime there are a number of ways to navigate to a forum you know exists but simply isn't directly listed in the top level category list.
In the case of the Forum Issues and GalCiv2 Site Issues forums if you can remember that they are subforums of the Off-topic forum then the easiest way to navigate to them is to use the pull down menu to the right of the main forum header as shown in the following screenshot.
Another interesting way to navigate the forums is to use the path indicators when you're in a forum as shown in the following screenshot, in this case from the GalCiv II forum (https://forums.galciv2.com/forum/162).
There are another three major ways to negotiate the forums besides these but they're a bit more obscure and I'll discuss them once I publish my data.
 Well they're not all that obscure or take that long to describe. The most straightforward is to "walk the tree" by entering each forum in turn, scrolling down to the bottom of that forum's recent post list to get to the sub category list and then continue down and back up each branch of the tree until the eintire site is negotiated. Tedious but it gets you to *most* forums on a particular site.
Another way is to go to any forum and then "create a post". From this screen there is a pulldown menu as to what category (i.e. forum) on the site that you wish to place the new post. This pulldown list will also list "hidden" top level forums that you would otherwise not know exist on the site. Sometimes the mere location in this pulldown list will be sufficient to tell you where the forum is, otherwise you'll have to do a test post and see where the post ends up.
The final method is to enter the https://forums.galciv2.com/forum/0 url. Forum 0 does not exist on GlaCiv2 (nor on any other site). When you try to view a non-existent forum on a particular site you actually get a list that contains the top level "hidden" forums. In many cases these forums are reachable by one of the more mundane methods but there are some forums that can only be found using this method (for example Demigod News http://forums.demigodthegame.com/forum/484 since it is both a top level hidden forum and it can't be posted to by normal citizens so it doesn't appear in the create post pulldown list.