6 files changed, 88 insertions, 20 deletions
diff --git a/MediaBrowser.Controller/Entities/BaseItem.cs b/MediaBrowser.Controller/Entities/BaseItem.cs
index 21a726aaec..209feac702 100644
--- a/MediaBrowser.Controller/Entities/BaseItem.cs
+++ b/MediaBrowser.Controller/Entities/BaseItem.cs
@@ -1546,15 +1546,27 @@ namespace MediaBrowser.Controller.Entities
             var extras = LibraryManager.FindExtras(item, fileSystemChildren, options.DirectoryService).ToArray();
             var newExtraIds = Array.ConvertAll(extras, x => x.Id);
 
-            var currentExtraIds = LibraryManager.GetItemList(new InternalItemsQuery()
+            var currentExtras = LibraryManager.GetItemList(new InternalItemsQuery()
             {
                 OwnerIds = [item.Id]
-            }).Select(e => e.Id).ToArray();
+            });
+
+            var currentExtraIds = currentExtras.Select(e => e.Id).ToArray();
 
             var extrasChanged = !currentExtraIds.OrderBy(x => x).SequenceEqual(newExtraIds.OrderBy(x => x));
 
             if (!extrasChanged && !options.ReplaceAllMetadata && options.MetadataRefreshMode != MetadataRefreshMode.FullRefresh)
             {
+                // The owner's dates may only have become known after its extras were created, so keep
+                // them in sync even when there is nothing to refresh.
+                foreach (var extra in currentExtras)
+                {
+                    if (extra.ExtraType is not null && InheritDatesFromOwner(item, extra))
+                    {
+                        await extra.UpdateToRepositoryAsync(ItemUpdateType.MetadataEdit, cancellationToken).ConfigureAwait(false);
+                    }
+                }
+
                 return false;
             }
 
@@ -1570,6 +1582,7 @@ namespace MediaBrowser.Controller.Entities
 
                 i.OwnerId = ownerId;
                 i.ParentId = Guid.Empty;
+
                 return RefreshMetadataForOwnedItem(i, true, subOptions, cancellationToken);
             });
 
@@ -2652,6 +2665,32 @@ namespace MediaBrowser.Controller.Entities
             }
         }
 
+        /// <summary>
+        /// Applies the owner's premiere date and production year to an owned item, returning whether anything changed.
+        /// </summary>
+        /// <param name="owner">The owner.</param>
+        /// <param name="ownedItem">The owned item.</param>
+        /// <returns><c>true</c> if the owned item was changed, else <c>false</c>.</returns>
+        internal static bool InheritDatesFromOwner(BaseItem owner, BaseItem ownedItem)
+        {
+            // Extras have no release date of their own, so the owner's is authoritative.
+            var changed = false;
+
+            if (owner.ProductionYear is not null && ownedItem.ProductionYear != owner.ProductionYear)
+            {
+                ownedItem.ProductionYear = owner.ProductionYear;
+                changed = true;
+            }
+
+            if (owner.PremiereDate is not null && ownedItem.PremiereDate != owner.PremiereDate)
+            {
+                ownedItem.PremiereDate = owner.PremiereDate;
+                changed = true;
+            }
+
+            return changed;
+        }
+
         protected async Task RefreshMetadataForOwnedItem(BaseItem ownedItem, bool copyTitleMetadata, MetadataRefreshOptions options, CancellationToken cancellationToken)
         {
             var newOptions = new MetadataRefreshOptions(options)
@@ -2711,6 +2750,11 @@ namespace MediaBrowser.Controller.Entities
                     ownedItem.CustomRating = item.CustomRating;
                     newOptions.ForceSave = true;
                 }
+
+                if (InheritDatesFromOwner(item, ownedItem))
+                {
+                    newOptions.ForceSave = true;
+                }
             }
 
             await ownedItem.RefreshMetadata(newOptions, cancellationToken).ConfigureAwait(false);
diff --git a/MediaBrowser.Controller/Entities/Movies/Movie.cs b/MediaBrowser.Controller/Entities/Movies/Movie.cs
index e8817a29cf..8c3ce2ff58 100644
--- a/MediaBrowser.Controller/Entities/Movies/Movie.cs
+++ b/MediaBrowser.Controller/Entities/Movies/Movie.cs
@@ -90,7 +90,7 @@ namespace MediaBrowser.Controller.Entities.Movies
         {
             var hasChanges = base.BeforeMetadataRefresh(replaceAllMetadata);
 
-            if (!ProductionYear.HasValue)
+            if (ProductionYear is null)
             {
                 var info = LibraryManager.ParseName(Name);
 
diff --git a/MediaBrowser.Controller/Entities/MusicVideo.cs b/MediaBrowser.Controller/Entities/MusicVideo.cs
index 237ad5198c..effbf98820 100644
--- a/MediaBrowser.Controller/Entities/MusicVideo.cs
+++ b/MediaBrowser.Controller/Entities/MusicVideo.cs
@@ -40,7 +40,7 @@ namespace MediaBrowser.Controller.Entities
         {
             var hasChanges = base.BeforeMetadataRefresh(replaceAllMetadata);
 
-            if (!ProductionYear.HasValue)
+            if (ProductionYear is null)
             {
                 var info = LibraryManager.ParseName(Name);
 
diff --git a/MediaBrowser.Controller/Entities/TV/Series.cs b/MediaBrowser.Controller/Entities/TV/Series.cs
index 952187c6e1..3ce241aca8 100644
--- a/MediaBrowser.Controller/Entities/TV/Series.cs
+++ b/MediaBrowser.Controller/Entities/TV/Series.cs
@@ -4,7 +4,6 @@
 
 using System;
 using System.Collections.Generic;
-using System.Globalization;
 using System.Linq;
 using System.Text.Json.Serialization;
 using System.Threading;
@@ -82,16 +81,23 @@ namespace MediaBrowser.Controller.Entities.TV
             {
                 var userdatakeys = GetUserDataKeys();
 
-                if (userdatakeys.Count > 1)
+                // The first user data key is a stable cross-folder identity.
+                // When none exists, fall back to the (normalized) series name.
+                var groupingKey = userdatakeys.Count > 1
+                    ? userdatakeys[0]
+                    : GetNameBasedGroupingKey();
+
+                if (!string.IsNullOrEmpty(groupingKey))
                 {
-                    return AddLibrariesToPresentationUniqueKey(userdatakeys[0]);
+                    return AppendPreferredLanguage(groupingKey);
                 }
             }
 
             return base.CreatePresentationUniqueKey();
         }
 
-        private string AddLibrariesToPresentationUniqueKey(string key)
+        // The owning libraries are deliberately NOT part of the key.
+        private string AppendPreferredLanguage(string key)
         {
             var lang = GetPreferredMetadataLanguage();
             if (!string.IsNullOrEmpty(lang))
@@ -99,16 +105,15 @@ namespace MediaBrowser.Controller.Entities.TV
                 key += "-" + lang;
             }
 
-            var folders = LibraryManager.GetCollectionFolders(this)
-                .Select(i => i.Id.ToString("N", CultureInfo.InvariantCulture))
-                .ToArray();
-
-            if (folders.Length == 0)
-            {
-                return key;
-            }
+            return key;
+        }
 
-            return key + "-" + string.Join('-', folders);
+        private string GetNameBasedGroupingKey()
+        {
+            // Prefix with the type so a series can never collide with a same-named item of another kind.
+            return string.IsNullOrEmpty(Name)
+                ? null
+                : "series-" + Name.ToLowerInvariant();
         }
 
         private static string GetUniqueSeriesKey(BaseItem series)
@@ -188,6 +193,25 @@ namespace MediaBrowser.Controller.Entities.TV
             return list;
         }
 
+        /// <inheritdoc />
+        protected override Guid[] GetExtraOwnerIds()
+        {
+            if (!LibraryManager.GetLibraryOptions(this).EnableAutomaticSeriesGrouping)
+            {
+                return base.GetExtraOwnerIds();
+            }
+
+            // Setting PresentationUniqueKey on the query disables presentation-key grouping, so this
+            // returns every folder-item of the merged series rather than the collapsed survivor.
+            var ids = LibraryManager.GetItemIds(new InternalItemsQuery
+            {
+                PresentationUniqueKey = GetPresentationUniqueKey(),
+                IncludeItemTypes = [BaseItemKind.Series]
+            });
+
+            return ids.Count == 0 ? base.GetExtraOwnerIds() : ids.ToArray();
+        }
+
         public override IReadOnlyList<BaseItem> GetChildren(User user, bool includeLinkedChildren, InternalItemsQuery query)
         {
             return GetSeasons(user, new DtoOptions(true));
@@ -507,7 +531,7 @@ namespace MediaBrowser.Controller.Entities.TV
         {
             var hasChanges = base.BeforeMetadataRefresh(replaceAllMetadata);
 
-            if (!ProductionYear.HasValue)
+            if (ProductionYear is null)
             {
                 var info = LibraryManager.ParseName(Name);
 
diff --git a/MediaBrowser.Controller/Entities/Trailer.cs b/MediaBrowser.Controller/Entities/Trailer.cs
index 939709215c..a2465eedf0 100644
--- a/MediaBrowser.Controller/Entities/Trailer.cs
+++ b/MediaBrowser.Controller/Entities/Trailer.cs
@@ -49,7 +49,7 @@ namespace MediaBrowser.Controller.Entities
         {
             var hasChanges = base.BeforeMetadataRefresh(replaceAllMetadata);
 
-            if (!ProductionYear.HasValue)
+            if (ProductionYear is null)
             {
                 var info = LibraryManager.ParseName(Name);
 
diff --git a/MediaBrowser.Controller/Entities/UserViewBuilder.cs b/MediaBrowser.Controller/Entities/UserViewBuilder.cs
index c57ed2faf8..9ba103cc8b 100644
--- a/MediaBrowser.Controller/Entities/UserViewBuilder.cs
+++ b/MediaBrowser.Controller/Entities/UserViewBuilder.cs
@@ -730,7 +730,7 @@ namespace MediaBrowser.Controller.Entities
             // Apply year filter
             if (query.Years.Length > 0)
             {
-                if (!(item.ProductionYear.HasValue && query.Years.Contains(item.ProductionYear.Value)))
+                if (item.ProductionYear is null || !query.Years.Contains(item.ProductionYear.Value))
                 {
                     return false;
                 }