diff --git a/app/models/lettings_log.rb b/app/models/lettings_log.rb
index d93a173f9..e6df9e54a 100644
--- a/app/models/lettings_log.rb
+++ b/app/models/lettings_log.rb
@@ -54,11 +54,17 @@ class LettingsLog < Log
   scope :unresolved, -> { where(unresolved: true) }
   scope :filter_by_organisation, ->(org, _user = nil) { where(owning_organisation: org).or(where(managing_organisation: org)) }
   scope :duplicate_logs, lambda { |log|
-    visible.where(log.slice(*DUPLICATE_LOG_ATTRIBUTES))
-    .where.not(id: log.id)
-    .where.not("startdate IS NULL OR age1 IS NULL OR sex1 IS NULL OR ecstat1 IS NULL OR tcharge IS NULL OR needstype IS NULL")
-    .where("location_id = ? OR needstype = 1", log.location_id)
-    .where("postcode_full = ? OR needstype = 2", log.postcode_full)
+    visible
+      .where(log.slice(*DUPLICATE_LOG_ATTRIBUTES))
+      .where.not(id: log.id)
+      .where.not(startdate: nil)
+      .where.not(sex1: nil)
+      .where.not(ecstat1: nil)
+      .where.not(tcharge: nil)
+      .where.not(needstype: nil)
+      .where("age1 IS NOT NULL OR age1_known = 1")
+      .where("location_id = ? OR needstype = 1", log.location_id)
+      .where("postcode_full = ? OR needstype = 2", log.postcode_full)
   }
 
   AUTOGENERATED_FIELDS = %w[id status created_at updated_at discarded_at].freeze
@@ -68,7 +74,7 @@ class LettingsLog < Log
   NUM_OF_WEEKS_FROM_PERIOD = { 2 => 26, 3 => 13, 4 => 12, 5 => 50, 6 => 49, 7 => 48, 8 => 47, 9 => 46, 1 => 52, 10 => 53 }.freeze
   SUFFIX_FROM_PERIOD = { 2 => "every 2 weeks", 3 => "every 4 weeks", 4 => "every month" }.freeze
   RETIREMENT_AGES = { "M" => 67, "F" => 60, "X" => 67 }.freeze
-  DUPLICATE_LOG_ATTRIBUTES = %w[tenancycode startdate age1 sex1 ecstat1 tcharge].freeze
+  DUPLICATE_LOG_ATTRIBUTES = %w[tenancycode startdate age1_known age1 sex1 ecstat1 tcharge].freeze
 
   def form
     FormHandler.instance.get_form(form_name) || FormHandler.instance.current_lettings_form
diff --git a/app/models/sales_log.rb b/app/models/sales_log.rb
index 311ecc565..ae76e32c3 100644
--- a/app/models/sales_log.rb
+++ b/app/models/sales_log.rb
@@ -44,12 +44,16 @@ class SalesLog < Log
   scope :duplicate_logs, lambda { |log|
     visible.where(log.slice(*DUPLICATE_LOG_ATTRIBUTES))
     .where.not(id: log.id)
-    .where.not("saledate is NULL OR age1 IS NULL OR sex1 IS NULL OR ecstat1 IS NULL OR postcode_full IS NULL")
+    .where.not(saledate: nil)
+    .where.not(sex1: nil)
+    .where.not(ecstat1: nil)
+    .where.not(postcode_full: nil)
+    .where("age1 IS NOT NULL OR age1_known = 1 OR age1_known = 2")
   }
 
   OPTIONAL_FIELDS = %w[purchid othtype].freeze
   RETIREMENT_AGES = { "M" => 65, "F" => 60, "X" => 65 }.freeze
-  DUPLICATE_LOG_ATTRIBUTES = %w[purchid saledate age1 sex1 ecstat1 postcode_full].freeze
+  DUPLICATE_LOG_ATTRIBUTES = %w[purchid saledate age1_known age1 sex1 ecstat1 postcode_full].freeze
 
   def lettings?
     false
diff --git a/spec/models/lettings_log_spec.rb b/spec/models/lettings_log_spec.rb
index 4912ebbe6..edc50bb10 100644
--- a/spec/models/lettings_log_spec.rb
+++ b/spec/models/lettings_log_spec.rb
@@ -2896,6 +2896,15 @@ RSpec.describe LettingsLog do
         end
       end
 
+      context "when there is a log with age1 not known" do
+        let!(:age1_not_known) { create(:lettings_log, :duplicate, age1_known: 1, age1: nil) }
+
+        it "returns the log as a duplicate if age1 is not known" do
+          log.update!(age1_known: 1, age1: nil)
+          expect(described_class.duplicate_logs(log)).to include(age1_not_known)
+        end
+      end
+
       context "when there is a duplicate supported housing log" do
         let(:scheme) { create(:scheme) }
         let(:location) { create(:location, scheme:) }
diff --git a/spec/models/sales_log_spec.rb b/spec/models/sales_log_spec.rb
index c382c364b..d032293c8 100644
--- a/spec/models/sales_log_spec.rb
+++ b/spec/models/sales_log_spec.rb
@@ -249,6 +249,33 @@ RSpec.describe SalesLog, type: :model do
         expect(described_class.duplicate_logs(log)).to include(purchid_not_given)
       end
     end
+
+    context "when there is a log age not known" do
+      let!(:age1_not_known) { create(:sales_log, :duplicate, age1_known: 1, age1: nil) }
+
+      it "returns the log as a duplicate if age is not known" do
+        log.update!(age1_known: 1, age1: nil)
+        expect(described_class.duplicate_logs(log)).to include(age1_not_known)
+      end
+    end
+
+    context "when there is a log age pefers not to say" do
+      let!(:age1_prefers_not_to_say) { create(:sales_log, :duplicate, age1_known: 2, age1: nil) }
+
+      it "returns the log as a duplicate if age is prefers not to say" do
+        log.update!(age1_known: 2, age1: nil)
+        expect(described_class.duplicate_logs(log)).to include(age1_prefers_not_to_say)
+      end
+    end
+
+    context "when there is a log age pefers not to say and not known" do
+      let!(:age1_prefers_not_to_say) { create(:sales_log, :duplicate, age1_known: 2, age1: nil) }
+
+      it "does not return the log as a duplicate if age is prefers not to say" do
+        log.update!(age1_known: 1, age1: nil)
+        expect(described_class.duplicate_logs(log)).not_to include(age1_prefers_not_to_say)
+      end
+    end
   end
 
   describe "derived variables" do