diff --git a/src/Microsoft.TestPlatform.CrossPlatEngine/Client/Parallel/DiscoveryDataAggregator.cs b/src/Microsoft.TestPlatform.CrossPlatEngine/Client/Parallel/DiscoveryDataAggregator.cs
index 581c5b058d..43a42d0d79 100644
--- a/src/Microsoft.TestPlatform.CrossPlatEngine/Client/Parallel/DiscoveryDataAggregator.cs
+++ b/src/Microsoft.TestPlatform.CrossPlatEngine/Client/Parallel/DiscoveryDataAggregator.cs
@@ -186,39 +186,44 @@ public void MarkSourcesWithStatus(IEnumerable<string?>? sources, DiscoveryStatus
 
         foreach (var source in sources)
         {
-            if (source is null)
+            MarkSourceWithStatus(source, status);
+        }
+    }
+
+    private void MarkSourceWithStatus(string? source, DiscoveryStatus status)
+    {
+        if (source is null)
+        {
+            return;
+        }
+
+        _sourcesWithDiscoveryStatus.AddOrUpdate(source,
+            _ =>
             {
-                continue;
-            }
+                if (status != DiscoveryStatus.NotDiscovered)
+                {
+                    EqtTrace.Warning($"DiscoveryDataAggregator.MarkSourcesWithStatus: Undiscovered {source} added with status: '{status}'.");
+                }
+                else
+                {
+                    EqtTrace.Verbose($"DiscoveryDataAggregator.MarkSourcesWithStatus: Adding {source} with status: '{status}'.");
+                }
 
-            _sourcesWithDiscoveryStatus.AddOrUpdate(source,
-                _ =>
+                return status;
+            },
+            (_, previousStatus) =>
+            {
+                if (previousStatus == DiscoveryStatus.FullyDiscovered && status != DiscoveryStatus.FullyDiscovered
+                    || previousStatus == DiscoveryStatus.PartiallyDiscovered && (status == DiscoveryStatus.NotDiscovered || status == DiscoveryStatus.SkippedDiscovery))
                 {
-                    if (status != DiscoveryStatus.NotDiscovered)
-                    {
-                        EqtTrace.Warning($"DiscoveryDataAggregator.MarkSourcesWithStatus: Undiscovered {source} added with status: '{status}'.");
-                    }
-                    else
-                    {
-                        EqtTrace.Verbose($"DiscoveryDataAggregator.MarkSourcesWithStatus: Adding {source} with status: '{status}'.");
-                    }
-
-                    return status;
-                },
-                (_, previousStatus) =>
+                    EqtTrace.Warning($"DiscoveryDataAggregator.MarkSourcesWithStatus: Downgrading source {source} status from '{previousStatus}' to '{status}'.");
+                }
+                else if (previousStatus != status)
                 {
-                    if (previousStatus == DiscoveryStatus.FullyDiscovered && status != DiscoveryStatus.FullyDiscovered
-                        || previousStatus == DiscoveryStatus.PartiallyDiscovered && (status == DiscoveryStatus.NotDiscovered || status == DiscoveryStatus.SkippedDiscovery))
-                    {
-                        EqtTrace.Warning($"DiscoveryDataAggregator.MarkSourcesWithStatus: Downgrading source {source} status from '{previousStatus}' to '{status}'.");
-                    }
-                    else if (previousStatus != status)
-                    {
-                        EqtTrace.Verbose($"DiscoveryDataAggregator.MarkSourcesWithStatus: Upgrading {source} status from '{previousStatus}' to '{status}'.");
-                    }
-                    return status;
-                });
-        }
+                    EqtTrace.Verbose($"DiscoveryDataAggregator.MarkSourcesWithStatus: Upgrading {source} status from '{previousStatus}' to '{status}'.");
+                }
+                return status;
+            });
     }
 
     /// <summary>
@@ -247,19 +252,19 @@ public void MarkSourcesWithStatus(IEnumerable<string?>? sources, DiscoveryStatus
         {
             var currentSource = testCase.Source;
 
-            // We rely on the fact that sources are processed in a sequential way, which
-            // means that when we receive a different source than the previous, we can
-            // assume that the previous source was fully discovered.
-            if (previousSource is null || previousSource == currentSource)
+            // Sources arrive sequentially; when source changes the previous one is fully discovered.
+            if (previousSource is null)
             {
-                MarkSourcesWithStatus(new[] { currentSource }, DiscoveryStatus.PartiallyDiscovered);
+                // First test case seen: mark this source as partially discovered.
+                MarkSourceWithStatus(currentSource, DiscoveryStatus.PartiallyDiscovered);
             }
             else if (currentSource != previousSource)
             {
                 EqtTrace.Verbose($"DiscoveryDataAggregator.MarkSourcesBasedOnDiscoveredTestCases: Discovered test source changed from {previousSource} to {currentSource}.");
-                MarkSourcesWithStatus(new[] { previousSource }, DiscoveryStatus.FullyDiscovered);
-                MarkSourcesWithStatus(new[] { currentSource }, DiscoveryStatus.PartiallyDiscovered);
+                MarkSourceWithStatus(previousSource, DiscoveryStatus.FullyDiscovered);
+                MarkSourceWithStatus(currentSource, DiscoveryStatus.PartiallyDiscovered);
             }
+            // When currentSource == previousSource: status already PartiallyDiscovered; skip.
 
             previousSource = currentSource;
         }