diff --git a/app/services/bulk_upload/lettings/year2023/row_parser.rb b/app/services/bulk_upload/lettings/year2023/row_parser.rb
index 9bd8eb8d2..381a90ee9 100644
--- a/app/services/bulk_upload/lettings/year2023/row_parser.rb
+++ b/app/services/bulk_upload/lettings/year2023/row_parser.rb
@@ -868,7 +868,8 @@ private
       errors.add(:field_8, error_message) # startdate
       errors.add(:field_9, error_message) # startdate
       errors.add(:field_13, error_message) # tenancycode
-      errors.add(location_field, error_message) if field_4 != 1 && location_field.present?# location
+      errors.add(location_field, error_message) if field_4 != 1 && location_field.present? # location
+      errors.add(:field_16, error_message) if field_4 != 1 && !location_field.present? # add to Scheme field as unclear whether log uses New or Old CORE ids
       errors.add(:field_23, error_message) if field_4 != 2 # postcode_full
       errors.add(:field_24, error_message) if field_4 != 2 # postcode_full
       errors.add(:field_25, error_message) if field_4 != 2 # la
diff --git a/spec/services/bulk_upload/lettings/year2023/row_parser_spec.rb b/spec/services/bulk_upload/lettings/year2023/row_parser_spec.rb
index cf2fc3c42..d87b3b45a 100644
--- a/spec/services/bulk_upload/lettings/year2023/row_parser_spec.rb
+++ b/spec/services/bulk_upload/lettings/year2023/row_parser_spec.rb
@@ -327,7 +327,7 @@ RSpec.describe BulkUpload::Lettings::Year2023::RowParser do
                 :field_8, # startdate
                 :field_9, # startdate
                 :field_13, # tenancycode
-                :field_17, # location
+                :field_16, # location
                 :field_46, # age1
                 :field_47, # sex1
                 :field_50, # ecstat1
@@ -343,6 +343,44 @@ RSpec.describe BulkUpload::Lettings::Year2023::RowParser do
           end
 
           context "with old core scheme and location ids" do
+            context "when a supported housing log already exists in the db" do
+              let(:attributes) { { bulk_upload:, field_4: "2", field_16: "123" } }
+
+              before do
+                parser.log.save!
+                parser.instance_variable_set(:@valid, nil)
+              end
+
+              it "is not a valid row" do
+                expect(parser).not_to be_valid
+              end
+
+              it "adds an error to all the fields used to determine duplicates" do
+                parser.valid?
+
+                error_message = "This is a duplicate log"
+
+                [
+                  :field_1, # owning_organisation
+                  :field_7, # startdate
+                  :field_8, # startdate
+                  :field_9, # startdate
+                  :field_13, # tenancycode
+                  :field_16, # location
+                  :field_46, # age1
+                  :field_47, # sex1
+                  :field_50, # ecstat1
+                  :field_132, # tcharge
+                ].each do |field|
+                  expect(parser.errors[field]).to include(error_message)
+                end
+
+                expect(parser.errors[:field_23]).not_to include(error_message)
+                expect(parser.errors[:field_24]).not_to include(error_message)
+                expect(parser.errors[:field_25]).not_to include(error_message)
+              end
+            end
+
             context "when a supported housing log with chcharges already exists in the db" do
               let(:bulk_upload) { create(:bulk_upload, :lettings, user:, needstype: 2) }
               let(:attributes) do
@@ -449,6 +487,44 @@ RSpec.describe BulkUpload::Lettings::Year2023::RowParser do
           end
 
           context "with new core scheme and location ids" do
+            context "when a supported housing log already exists in the db" do
+              let(:attributes) { { bulk_upload:, field_4: "2", field_16: "S123" } }
+
+              before do
+                parser.log.save!
+                parser.instance_variable_set(:@valid, nil)
+              end
+
+              it "is not a valid row" do
+                expect(parser).not_to be_valid
+              end
+
+              it "adds an error to all the fields used to determine duplicates" do
+                parser.valid?
+
+                error_message = "This is a duplicate log"
+
+                [
+                  :field_1, # owning_organisation
+                  :field_7, # startdate
+                  :field_8, # startdate
+                  :field_9, # startdate
+                  :field_13, # tenancycode
+                  :field_17, # location
+                  :field_46, # age1
+                  :field_47, # sex1
+                  :field_50, # ecstat1
+                  :field_132, # tcharge
+                ].each do |field|
+                  expect(parser.errors[field]).to include(error_message)
+                end
+
+                expect(parser.errors[:field_23]).not_to include(error_message)
+                expect(parser.errors[:field_24]).not_to include(error_message)
+                expect(parser.errors[:field_25]).not_to include(error_message)
+              end
+            end
+
             context "when a supported housing log with chcharges already exists in the db" do
               let(:bulk_upload) { create(:bulk_upload, :lettings, user:, needstype: 2) }
               let(:attributes) do