Currently only updated documents are recorded during a rollback. Insert operations are rolled back by deleting their documents, and are not recorded in a rollback file. Thus, they cannot be manually fixed when rollback data is merged to new primary. We could export a single bson file which lists the deleted documents (namespace + _id) in another file.

_Deleted_<ts>.bson:
{_id:ObjectId, ns:<ns>, deleted_id: <id>}