diff --git a/JustDummies.UnitTests/CompositionTests.cs b/JustDummies.UnitTests/CompositionTests.cs
index b6e0010..e7b54c4 100644
--- a/JustDummies.UnitTests/CompositionTests.cs
+++ b/JustDummies.UnitTests/CompositionTests.cs
@@ -155,6 +155,25 @@ public void CombineOverMixedForeignAndLibraryQualifiesTheHint() {
         Check.That(caught.Message).Not.Contains("The arbitrary values were seeded with");
     }
 
+    [Fact(DisplayName = "A composer failure over a Combine mixing two different seeded sources does not promise a full replay from one seed.")]
+    public void CombineOverMixedSeededSourcesQualifiesTheHint() {
+        // The first operand draws from Any.WithSeed(4242); the second from the ambient source. The composed value
+        // depends on BOTH, so replaying WithSeed(4242) alone reproduces only the first — the hint must not promise a
+        // deterministic full replay from that one seed (issue #319).
+        IAny<string> generator = Any.Combine<int, int, string>(
+            Any.WithSeed(4242).Int32().Between(1, 3),
+            Any.Int32().Between(4, 6),
+            (first, second) => throw new InvalidOperationException($"rejected {first}/{second}"));
+
+        AnyGenerationException caught = Assert.Throws<AnyGenerationException>(() => generator.Generate());
+
+        Check.That(caught.Message).Contains("Combine(...)");
+        Check.WithCustomMessage($"The hint over-promised a full replay. Message: {caught.Message}")
+             .That(caught.Message).Not.Contains("already replays deterministically");
+        Check.WithCustomMessage($"The hint did not qualify the replay promise. Message: {caught.Message}")
+             .That(caught.Message).Contains("not reproducible from this seed alone");
+    }
+
     [Fact(DisplayName = "Combine composes four through eight parts, passing every constrained part to the lambda.")]
     public void CombineSupportsHigherArities() {
         IAny<int> part = Any.Int32().Between(1, 9);
diff --git a/JustDummies/Any.cs b/JustDummies/Any.cs
index 5fed7a6..a64dbdb 100644
--- a/JustDummies/Any.cs
+++ b/JustDummies/Any.cs
@@ -613,7 +613,7 @@ public static IAny<TResult> Combine<T1, T2, TResult>(IAny<T1> first, IAny<T2> se
         if (compose is null) { throw new ArgumentNullException(nameof(compose)); }
 
         RandomSource? source       = AnyDerivation.SourceOf(first) ?? AnyDerivation.SourceOf(second);
-        bool          reproducible = AnyDerivation.IsReproducible(first) && AnyDerivation.IsReproducible(second);
+        bool          reproducible = AnyDerivation.DrawsOnlyFrom(first, source) && AnyDerivation.DrawsOnlyFrom(second, source);
 
         return new DerivedAny<TResult>(source, reproducible, () => {
             T1 firstValue  = first.Generate();
@@ -644,7 +644,7 @@ public static IAny<TResult> Combine<T1, T2, T3, TResult>(IAny<T1> first, IAny<T2
         if (compose is null) { throw new ArgumentNullException(nameof(compose)); }
 
         RandomSource? source       = AnyDerivation.SourceOf(first) ?? AnyDerivation.SourceOf(second) ?? AnyDerivation.SourceOf(third);
-        bool          reproducible = AnyDerivation.IsReproducible(first) && AnyDerivation.IsReproducible(second) && AnyDerivation.IsReproducible(third);
+        bool          reproducible = AnyDerivation.DrawsOnlyFrom(first, source) && AnyDerivation.DrawsOnlyFrom(second, source) && AnyDerivation.DrawsOnlyFrom(third, source);
 
         return new DerivedAny<TResult>(source, reproducible, () => {
             T1 firstValue  = first.Generate();
@@ -678,7 +678,7 @@ public static IAny<TResult> Combine<T1, T2, T3, T4, TResult>(IAny<T1> first, IAn
         if (compose is null) { throw new ArgumentNullException(nameof(compose)); }
 
         RandomSource? source       = AnyDerivation.SourceOf(first) ?? AnyDerivation.SourceOf(second) ?? AnyDerivation.SourceOf(third) ?? AnyDerivation.SourceOf(fourth);
-        bool          reproducible = AnyDerivation.IsReproducible(first) && AnyDerivation.IsReproducible(second) && AnyDerivation.IsReproducible(third) && AnyDerivation.IsReproducible(fourth);
+        bool          reproducible = AnyDerivation.DrawsOnlyFrom(first, source) && AnyDerivation.DrawsOnlyFrom(second, source) && AnyDerivation.DrawsOnlyFrom(third, source) && AnyDerivation.DrawsOnlyFrom(fourth, source);
 
         return new DerivedAny<TResult>(source, reproducible, () => {
             T1 firstValue  = first.Generate();
@@ -716,7 +716,7 @@ public static IAny<TResult> Combine<T1, T2, T3, T4, T5, TResult>(IAny<T1> first,
         if (compose is null) { throw new ArgumentNullException(nameof(compose)); }
 
         RandomSource? source       = AnyDerivation.SourceOf(first) ?? AnyDerivation.SourceOf(second) ?? AnyDerivation.SourceOf(third) ?? AnyDerivation.SourceOf(fourth) ?? AnyDerivation.SourceOf(fifth);
-        bool          reproducible = AnyDerivation.IsReproducible(first) && AnyDerivation.IsReproducible(second) && AnyDerivation.IsReproducible(third) && AnyDerivation.IsReproducible(fourth) && AnyDerivation.IsReproducible(fifth);
+        bool          reproducible = AnyDerivation.DrawsOnlyFrom(first, source) && AnyDerivation.DrawsOnlyFrom(second, source) && AnyDerivation.DrawsOnlyFrom(third, source) && AnyDerivation.DrawsOnlyFrom(fourth, source) && AnyDerivation.DrawsOnlyFrom(fifth, source);
 
         return new DerivedAny<TResult>(source, reproducible, () => {
             T1 firstValue  = first.Generate();
@@ -758,7 +758,7 @@ public static IAny<TResult> Combine<T1, T2, T3, T4, T5, T6, TResult>(IAny<T1> fi
         if (compose is null) { throw new ArgumentNullException(nameof(compose)); }
 
         RandomSource? source       = AnyDerivation.SourceOf(first) ?? AnyDerivation.SourceOf(second) ?? AnyDerivation.SourceOf(third) ?? AnyDerivation.SourceOf(fourth) ?? AnyDerivation.SourceOf(fifth) ?? AnyDerivation.SourceOf(sixth);
-        bool          reproducible = AnyDerivation.IsReproducible(first) && AnyDerivation.IsReproducible(second) && AnyDerivation.IsReproducible(third) && AnyDerivation.IsReproducible(fourth) && AnyDerivation.IsReproducible(fifth) && AnyDerivation.IsReproducible(sixth);
+        bool          reproducible = AnyDerivation.DrawsOnlyFrom(first, source) && AnyDerivation.DrawsOnlyFrom(second, source) && AnyDerivation.DrawsOnlyFrom(third, source) && AnyDerivation.DrawsOnlyFrom(fourth, source) && AnyDerivation.DrawsOnlyFrom(fifth, source) && AnyDerivation.DrawsOnlyFrom(sixth, source);
 
         return new DerivedAny<TResult>(source, reproducible, () => {
             T1 firstValue  = first.Generate();
@@ -806,7 +806,7 @@ public static IAny<TResult> Combine<T1, T2, T3, T4, T5, T6, T7, TResult>(IAny<T1
         if (compose is null) { throw new ArgumentNullException(nameof(compose)); }
 
         RandomSource? source       = AnyDerivation.SourceOf(first) ?? AnyDerivation.SourceOf(second) ?? AnyDerivation.SourceOf(third) ?? AnyDerivation.SourceOf(fourth) ?? AnyDerivation.SourceOf(fifth) ?? AnyDerivation.SourceOf(sixth) ?? AnyDerivation.SourceOf(seventh);
-        bool          reproducible = AnyDerivation.IsReproducible(first) && AnyDerivation.IsReproducible(second) && AnyDerivation.IsReproducible(third) && AnyDerivation.IsReproducible(fourth) && AnyDerivation.IsReproducible(fifth) && AnyDerivation.IsReproducible(sixth) && AnyDerivation.IsReproducible(seventh);
+        bool          reproducible = AnyDerivation.DrawsOnlyFrom(first, source) && AnyDerivation.DrawsOnlyFrom(second, source) && AnyDerivation.DrawsOnlyFrom(third, source) && AnyDerivation.DrawsOnlyFrom(fourth, source) && AnyDerivation.DrawsOnlyFrom(fifth, source) && AnyDerivation.DrawsOnlyFrom(sixth, source) && AnyDerivation.DrawsOnlyFrom(seventh, source);
 
         return new DerivedAny<TResult>(source, reproducible, () => {
             T1 firstValue   = first.Generate();
@@ -859,7 +859,7 @@ public static IAny<TResult> Combine<T1, T2, T3, T4, T5, T6, T7, T8, TResult>(IAn
         if (compose is null) { throw new ArgumentNullException(nameof(compose)); }
 
         RandomSource? source       = AnyDerivation.SourceOf(first) ?? AnyDerivation.SourceOf(second) ?? AnyDerivation.SourceOf(third) ?? AnyDerivation.SourceOf(fourth) ?? AnyDerivation.SourceOf(fifth) ?? AnyDerivation.SourceOf(sixth) ?? AnyDerivation.SourceOf(seventh) ?? AnyDerivation.SourceOf(eighth);
-        bool          reproducible = AnyDerivation.IsReproducible(first) && AnyDerivation.IsReproducible(second) && AnyDerivation.IsReproducible(third) && AnyDerivation.IsReproducible(fourth) && AnyDerivation.IsReproducible(fifth) && AnyDerivation.IsReproducible(sixth) && AnyDerivation.IsReproducible(seventh) && AnyDerivation.IsReproducible(eighth);
+        bool          reproducible = AnyDerivation.DrawsOnlyFrom(first, source) && AnyDerivation.DrawsOnlyFrom(second, source) && AnyDerivation.DrawsOnlyFrom(third, source) && AnyDerivation.DrawsOnlyFrom(fourth, source) && AnyDerivation.DrawsOnlyFrom(fifth, source) && AnyDerivation.DrawsOnlyFrom(sixth, source) && AnyDerivation.DrawsOnlyFrom(seventh, source) && AnyDerivation.DrawsOnlyFrom(eighth, source);
 
         return new DerivedAny<TResult>(source, reproducible, () => {
             T1 firstValue   = first.Generate();
diff --git a/JustDummies/AnyDerivation.cs b/JustDummies/AnyDerivation.cs
index 27ace87..f7466ca 100644
--- a/JustDummies/AnyDerivation.cs
+++ b/JustDummies/AnyDerivation.cs
@@ -69,6 +69,18 @@ internal static bool IsReproducible<T>(IAny<T> generator) {
         return SourceOf(generator) is not null;
     }
 
+    /// <summary>
+    ///     Whether <paramref name="generator" /> is reproducible <b>and</b> draws from <paramref name="source" />
+    ///     specifically — the per-operand condition for a <c>Combine</c>'s full-replay promise. An operand that is
+    ///     individually reproducible but draws from a <i>different</i> seeded source (a second <see cref="Any.WithSeed" />
+    ///     context, or the ambient source alongside a fixed one) leaves the reported seed covering only part of the run,
+    ///     so naming it as a deterministic full replay would over-promise. When the operands do not all draw from the one
+    ///     reported source, the hint is qualified instead — exactly as it is for a foreign operand.
+    /// </summary>
+    internal static bool DrawsOnlyFrom<T>(IAny<T> generator, RandomSource? source) {
+        return IsReproducible(generator) && ReferenceEquals(SourceOf(generator), source);
+    }
+
     /// <summary>
     ///     A conservative upper bound on the number of distinct values <paramref name="generator" /> yields, when it
     ///     advertises one through <see cref="ICardinalityHint{T}" />; <c>null</c> when the domain is unbounded or unknown.