diff --git a/experimenter/experimenter/jetstream/client.py b/experimenter/experimenter/jetstream/client.py
index 5fc4ba5f1..c0d77b200 100644
--- a/experimenter/experimenter/jetstream/client.py
+++ b/experimenter/experimenter/jetstream/client.py
@@ -287,11 +287,29 @@ def get_experiment_data(experiment: NimbusExperiment):
             if data and window == AnalysisWindow.OVERALL:
                 # Append some values onto the incoming Jetstream data
                 data.append_population_percentages()
-                data.append_retention_data(
+                week_2_retention = data.get_retention_by_window(
+                    2,
                     raw_data.get(AnalysisWindow.WEEKLY, {})
                     .get(AnalysisBasis.ENROLLMENTS, {})
-                    .get(segment)
+                    .get(segment),
+                    Metric.RETENTION,
                 )
+                if not week_2_retention:
+                    runtime_errors.append(
+                        AnalysisError(
+                            experiment=experiment.slug,
+                            filename="experimenter/jetstream/client.py",
+                            func_name="get_experiment_data",
+                            log_level="WARNING",
+                            message=(
+                                "Week 2 retention is unavailable because this "
+                                "experiment did not run long enough."
+                            ),
+                            metric=Metric.RETENTION,
+                            timestamp=timezone.now(),
+                        )
+                    )
+                data.extend(week_2_retention)
                 # Append 3-day retention from daily data
                 data.append_retention_3_days(
                     raw_data.get(AnalysisWindow.DAILY, {})
@@ -307,6 +325,12 @@ def get_experiment_data(experiment: NimbusExperiment):
                 if segment == Segment.ALL:
                     experiment_data["other_metrics"] = other_metrics
             elif data and window == AnalysisWindow.WEEKLY:
+                data.replace_retention_weeks(
+                    raw_data.get(AnalysisWindow.WEEKLY, {})
+                    .get(AnalysisBasis.ENROLLMENTS, {})
+                    .get(segment)
+                )
+
                 # Append 3-day retention from daily data
                 data.append_retention_3_days(
                     raw_data.get(AnalysisWindow.DAILY, {})
@@ -370,6 +394,12 @@ def get_experiment_data(experiment: NimbusExperiment):
                 if segment == Segment.ALL:
                     experiment_data["other_metrics"].update(other_metrics)
             elif data and window == AnalysisWindow.WEEKLY:
+                data.replace_retention_weeks(
+                    raw_data.get(AnalysisWindow.WEEKLY, {})
+                    .get(AnalysisBasis.EXPOSURES, {})
+                    .get(segment)
+                )
+
                 # Append 3-day retention from daily data
                 data.append_retention_3_days(
                     raw_data.get(AnalysisWindow.DAILY, {})
@@ -421,14 +451,17 @@ def get_experiment_data(experiment: NimbusExperiment):
                     errors_experiment_overall.append(err)
 
     for e in runtime_errors:
-        analysis_error = AnalysisError(
-            experiment=experiment.slug,
-            filename="experimenter/jetstream/client.py",
-            func_name="load_data_from_gcs",
-            log_level="WARNING",
-            message=e,
-            timestamp=timezone.now(),
-        )
+        if isinstance(e, AnalysisError):
+            analysis_error = e
+        else:
+            analysis_error = AnalysisError(
+                experiment=experiment.slug,
+                filename="experimenter/jetstream/client.py",
+                func_name="load_data_from_gcs",
+                log_level="WARNING",
+                message=e,
+                timestamp=timezone.now(),
+            )
         errors_experiment_overall.append(analysis_error.model_dump())
 
     errors_by_metric["experiment"] = errors_experiment_overall
diff --git a/experimenter/experimenter/jetstream/models.py b/experimenter/experimenter/jetstream/models.py
index bb7c620fc..fa8b9a7d0 100644
--- a/experimenter/experimenter/jetstream/models.py
+++ b/experimenter/experimenter/jetstream/models.py
@@ -77,6 +77,7 @@ class Group(StrEnum):
     Group.SEARCH: SEARCH_METRICS,
     Group.USAGE: USAGE_METRICS,
 }
+RETENTION_2_WEEKS_WINDOW_INDEX = 2
 RETENTION_3_DAYS_WINDOW_INDEX = 4
 
 
@@ -155,14 +156,24 @@ def get_retention_by_window(self, window_index, data, metric):
         ]
 
     def append_retention_data(self, weekly_data):
-        # Try to get the two-week retention data. If it doesn't
-        # exist (experiment was too short), settle for 1 week.
-        retention_data = self.get_retention_by_window(2, weekly_data, Metric.RETENTION)
-        if len(retention_data) == 0:
-            retention_data = self.get_retention_by_window(
-                1, weekly_data, Metric.RETENTION
-            )
+        # Only use two-week retention data.
+        retention_data = self.get_retention_by_window(
+            RETENTION_2_WEEKS_WINDOW_INDEX, weekly_data, Metric.RETENTION
+        )
+
+        self.extend(retention_data)
+
+    def replace_retention_weeks(self, weekly_data):
+        # Remove all weekly retention data except for week 2.
+        retention_data = self.get_retention_by_window(
+            RETENTION_2_WEEKS_WINDOW_INDEX, weekly_data, Metric.RETENTION
+        )
 
+        self.root = [
+            jetstream_data_point
+            for jetstream_data_point in self.root
+            if jetstream_data_point.metric != Metric.RETENTION
+        ]
         self.extend(retention_data)
 
     def append_retention_3_days(self, daily_data):
diff --git a/experimenter/experimenter/jetstream/tests/test_jetstream_data.py b/experimenter/experimenter/jetstream/tests/test_jetstream_data.py
index 56481a790..44a4477f5 100644
--- a/experimenter/experimenter/jetstream/tests/test_jetstream_data.py
+++ b/experimenter/experimenter/jetstream/tests/test_jetstream_data.py
@@ -61,6 +61,75 @@ def test_append_retention_3_days_extracts_data(self):
 
         self.assertIn(retention, data)
 
+    def test_append_retention_data_ignores_week_1_only_data(self):
+        week_1_retention = JetstreamDataPoint(
+            metric=Metric.RETENTION,
+            statistic=Statistic.BINOMIAL,
+            branch="control",
+            point=0.65,
+            segment=Segment.ALL,
+            window_index="1",
+        )
+
+        data = JetstreamData([])
+        data.append_retention_data([week_1_retention])
+
+        self.assertNotIn(week_1_retention, data)
+
+    def test_append_retention_data_uses_week_2_data(self):
+        week_2_retention = JetstreamDataPoint(
+            metric=Metric.RETENTION,
+            statistic=Statistic.BINOMIAL,
+            branch="control",
+            point=0.65,
+            segment=Segment.ALL,
+            window_index="2",
+        )
+
+        data = JetstreamData([])
+        data.append_retention_data([week_2_retention])
+
+        self.assertIn(week_2_retention, data)
+
+    def test_replace_retention_replaces_existing_entries(self):
+        existing_retention_1 = JetstreamDataPoint(
+            metric=Metric.RETENTION,
+            statistic=Statistic.BINOMIAL,
+            branch="control",
+            point=0.5,
+            segment=Segment.ALL,
+            window_index="1",
+        )
+        kept_retention = JetstreamDataPoint(
+            metric=Metric.RETENTION_3_DAYS,
+            statistic=Statistic.BINOMIAL,
+            branch="control",
+            point=0.25,
+            segment=Segment.ALL,
+            window_index="2",
+        )
+        existing_retention_2 = JetstreamDataPoint(
+            metric=Metric.RETENTION_3_DAYS,
+            statistic=Statistic.BINOMIAL,
+            branch="control",
+            point=0.25,
+            segment=Segment.ALL,
+            window_index="3",
+        )
+
+        data = JetstreamData(
+            [
+                existing_retention_1,
+                kept_retention,
+                existing_retention_2,
+            ]
+        )
+        data.replace_retention_3_days(data)
+
+        self.assertNotIn(existing_retention_1, data)
+        self.assertNotIn(existing_retention_2, data)
+        self.assertIn(kept_retention, data)
+
     def test_replace_retention_3_days_replaces_existing_entries(self):
         existing_retention_1 = JetstreamDataPoint(
             metric=Metric.RETENTION_3_DAYS,