
Afaik before 1.20, even though they were in the game files, the conditions for generating them were never fulfilled. I assumed this was because they were a relic from some older development version, since you don't need to play stratagems to declare war in the current game. Declaring war through the cards doesn't give you the screen where you can view the declaration's effects either.
Only use I can think for them is the edge case where you want to declare war on someone you don't have a border with? Or is that exactly why they were enabled now, something to do with naval landings?