Hello.
At the moment (if I have this right), the document suffix only appears if you compile the whole manuscript.
It might be handy to have an option of adding the suffix for partial compiles.
Why?
Well, if you just submit bits of the manuscript for review (I’m in a writing group), then it’s handy to be able to put a couple of stars along the bottom so other group members know that this is the end of the excerpt.
Okay, we can drop this one. Turns out it’s not needed.
There’s a compile option that appears when you compile a section of the document:
[x] Treat compile group as complete document
Selecting this will compile the group as if it were the whole book, which means the document suffix appears at the very end.
As you were. 
Glad you found it!
Ah, nearly, but not quite.
Seems to be one of those either/or situations.
If I set to compile the selection as a complete document, then it’s numbered from chapter one, but I lose the end of document marker at the end.
If I select a single chapter and compile it, then I have the chapter numbered correctly, but no end of document marker.
Is there any way to get the chapters numbered correctly, and the end of document marker?
Create a document that contains only your end of document marker. Give it a Section Layout that compiles it ‘as-is,’ with just the text, no title. Add to Compile contents as needed.
Katherine
Yes, that would work, and fiddling with the structure isn’t too difficult.