To make things a little easier, here is a page to allow you to view the theories by series title. Any theory that crosses into a specific game will be tagged with that game’s title.
If a game has been released in English (or has an English announcement), the English title will be the tag used. If it is still a Japanese only game, it will have its Japanese only title. (Trails in the Sky FC, Trails in the Sky SC, Sora no Kiseki the 3rd, as an example.)
As a note, some theories may cross over multiple games.
You can view the posts for each of the tags below:
Trails in the Sky FC
Trails in the Sky SC
Trails in the Sky the 3rd
Zero no Kiseki
Ao no Kiseki
Trails of Cold Steel
Trails of Cold Steel II
Trails of Cold Steel III (Listed as Sen no Kiseki III until localization announcement.)
If you get a 404 error when loading the tag, that simply means that there are no posts for it yet.