When writing for horns I usually write in one staff with pianosound and later explode to several staffs to make the parts.
Often there are unison passages that split into harmony, but when exploding the unison passages is only copied to the top staff.
There must be a setting to copy/explode to all staffs?
(It's takes a lot of time finding all the missing/ unison and copy/ drag them. Even worse, so easy to miss..)
MBP 10.12, Finale 25