#servant arrival

It’s a mix of both. If they come out of nowhere with little references, I see where they fit in the grand scheme of things on the spot. If they’re someone who’s been mentioned or appeared in the Fate/Series somewhere (like Strange Fake, Extella, etc.), then they likely have at least some tentative plans that will see adjustment. Whether or not they wind up popping up sooner rather than later depends on circumstances, story issues, and compatibility. 

Supplement 3 and 4 follow one after the other, and are both smaller than the typical supplement. 4 will definitely uphold the tradition, but 3 gets a pass for obvious reasons. As for whether or not one will wind up being lost in Supplement 3… well, we all know what’s coming.