When creating a copy of a Family Instance, the "Key Attribute used for comparing" in the Revit Family instance Parameter (used in the Active / Default Occurrence <-> Revit Instance Configuration) is cleared out. This will ensure that the new Family Instance will not contain a duplicate for the value that is meant to be unique for the dRofus syncing function.
In the following example, "Identity Data: drofus_occurrence_id" is Revit's parameter used as the "Key Attribute for comparing" within the Default Configuration:
This means that if a Revit User was to create a new Instance of "Table_Coffee_Eames_FUR" by either clicking on "Copy" or "Create Similar", while the highlighted Instance has already been linked to a dRofus Occurrence (using "drofus_occurrence_id" = 52314) as follows:
..... the new Family Instance will have "drofus_occurrence_id" = <blank> as follows:
This will ensure that no two or more Family Instances (created by either the "Copy" or "Create Similar command) will have the same value as the "Key Attribute used for comparing", meaning the link between the (originally linked) Family Instance and the corresponding dRofus Occurrence will never be lost.