OK - sorry to be the cause of so much work. I might continue to try to make sense of it here but please don’t worry about it further.
I’ve just discovered that if I run:
tell application id "DNtp"
activate
close every think window
end tell
and then run:
tell application id "DNtp"
activate
close every think window
load workspace "Diaries"
end tell
I do not get duplicate windows (i.e., when launching from an open but windowless DT).
Let’s leave it! Thanks for all your work, though.