Is there an easy way to prevent a form from creating a duplicate when submitting a saved form?
Well, if you were managing documents instead of Forms you would use 'Require Check-in'. However, this post suggests using versioning to manage the issue instead.
You also have to think about how each Form (item) is named - a 'naming convention'. If each item is named you can prevent duplicates from being saved. Go in list settings>select one a column (e.g. Title)>Enforce Unique Values. This will prevent a new item being saved using the same value. The Value 'format' can be defined by site admin e.g. 2017-11-24-A, the next item is saved as 2017-11-24-B and so on.