I\'d like a recipe for finding duplicated changes. patch-id is likely to be the same but the commit attributes may not be.
This seems to be an intended use of patch-
Because the duplicate changes are likely to be not on the same branch (except when there are reverts in between them), you could use git cherry:
git cherry [-v] [<upstream> [<head> [<limit>]]]
Where upstream would be the branch to check for duplicates of changes in head.
upstream
head