diff --git a/app/controllers/api/submissions_controller.rb b/app/controllers/api/submissions_controller.rb
index 1ae634e67..bda564c0c 100644
--- a/app/controllers/api/submissions_controller.rb
+++ b/app/controllers/api/submissions_controller.rb
@@ -74,8 +74,8 @@ def create
       Submissions.send_signature_requests(submissions)
 
       submissions.each do |submission|
-        if submission.submitters.all?(&:completed_at?) && submission.submitters.last
-          ProcessSubmitterCompletionJob.perform_async({ 'submitter_id' => submission.submitters.last.id })
+        submission.submitters.each do |submitter|
+          ProcessSubmitterCompletionJob.perform_async({ 'submitter_id' => submitter.id }) if submitter.completed_at?
         end
       end
 
diff --git a/app/jobs/process_submitter_completion_job.rb b/app/jobs/process_submitter_completion_job.rb
index 56ed4c5df..19c278d64 100644
--- a/app/jobs/process_submitter_completion_job.rb
+++ b/app/jobs/process_submitter_completion_job.rb
@@ -6,6 +6,8 @@ class ProcessSubmitterCompletionJob
   def perform(params = {})
     submitter = Submitter.find(params['submitter_id'])
 
+    create_completed_submitter!(submitter)
+
     is_all_completed = !submitter.submission.submitters.exists?(completed_at: nil)
 
     if !is_all_completed && submitter.submission.submitters_order_preserved?
@@ -24,7 +26,7 @@ def perform(params = {})
       enqueue_completed_emails(submitter)
     end
 
-    create_completed_submitter!(submitter)
+    create_completed_documents!(submitter)
 
     enqueue_completed_webhooks(submitter, is_all_completed:)
   end
@@ -45,15 +47,19 @@ def create_completed_submitter!(submitter)
       completed_at: submitter.completed_at
     )
 
-    submitter.documents.each do |attachment|
-      next if attachment.metadata['sha256'].blank?
-
-      completed_submitter.completed_documents << CompletedDocument.new(sha256: attachment.metadata['sha256'])
-    end
-
     completed_submitter.save!
 
     completed_submitter
+  rescue ActiveRecord::RecordNotUnique
+    retry
+  end
+
+  def create_completed_documents!(submitter)
+    submitter.documents.filter_map do |attachment|
+      next if attachment.metadata['sha256'].blank?
+
+      CompletedDocument.find_or_create_by!(sha256: attachment.metadata['sha256'], submitter_id: submitter.id)
+    end
   end
 
   def enqueue_completed_webhooks(submitter, is_all_completed: false)
diff --git a/app/models/completed_document.rb b/app/models/completed_document.rb
index 2c842e291..5ec53ca44 100644
--- a/app/models/completed_document.rb
+++ b/app/models/completed_document.rb
@@ -16,7 +16,7 @@
 #  index_completed_documents_on_submitter_id  (submitter_id)
 #
 class CompletedDocument < ApplicationRecord
-  belongs_to :submitter
+  belongs_to :submitter, optional: true
 
   has_one :completed_submitter, primary_key: :submitter_id, inverse_of: :completed_documents, dependent: :destroy
 end
diff --git a/app/models/completed_submitter.rb b/app/models/completed_submitter.rb
index 181f2241f..e34f65d2e 100644
--- a/app/models/completed_submitter.rb
+++ b/app/models/completed_submitter.rb
@@ -18,7 +18,7 @@
 # Indexes
 #
 #  index_completed_submitters_on_account_id    (account_id)
-#  index_completed_submitters_on_submitter_id  (submitter_id)
+#  index_completed_submitters_on_submitter_id  (submitter_id) UNIQUE
 #
 class CompletedSubmitter < ApplicationRecord
   belongs_to :submitter
diff --git a/db/migrate/20241026161207_add_unique_index_on_completed_submitters.rb b/db/migrate/20241026161207_add_unique_index_on_completed_submitters.rb
new file mode 100644
index 000000000..30b47c986
--- /dev/null
+++ b/db/migrate/20241026161207_add_unique_index_on_completed_submitters.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+class AddUniqueIndexOnCompletedSubmitters < ActiveRecord::Migration[7.2]
+  def change
+    remove_index :completed_submitters, :submitter_id
+    add_index :completed_submitters, :submitter_id, unique: true
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 556514761..3fd0ab117 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.2].define(version: 2024_10_22_125135) do
+ActiveRecord::Schema[7.2].define(version: 2024_10_26_161207) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
 
@@ -109,7 +109,7 @@
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.index ["account_id"], name: "index_completed_submitters_on_account_id"
-    t.index ["submitter_id"], name: "index_completed_submitters_on_submitter_id"
+    t.index ["submitter_id"], name: "index_completed_submitters_on_submitter_id", unique: true
   end
 
   create_table "document_generation_events", force: :cascade do |t|