docs: clarify named storage schema APIs

astro/src/content/docs/identityserver/data/providers/duende-storage/databases/index.mdx

@@ -89,8 +89,11 @@ Duende Storage separates two kinds of schema change:
   opening a database connection. Pass `DatabaseSchemaVersion.Zero` for the full script from an empty database.
 
 `app.Services.GetRequiredService<IStorageInstanceSchema>()` resolves the default storage instance only. For a named
-instance, use `IStorageInstanceSchemaFactory.GetStorageInstanceSchema(storageInstanceId, cancellationToken)` to resolve its schema,
-as shown in [Multiple Storage Instances](/identityserver/data/providers/duende-storage/multiple-storage-instances.md).
+instance, resolve `IStorageInstanceSchemaFactory` and call
+`GetStorageInstanceSchema(storageInstanceId, cancellationToken)`. The returned schema provides the same migration,
+version-checking, verification, and script-generation operations for that named instance. See
+[Multiple Storage Instances](/identityserver/data/providers/duende-storage/multiple-storage-instances.md) for a
+complete registration and migration example.
 
 ### If a Migration Fails
 

astro/src/content/docs/identityserver/data/providers/duende-storage/getting-started.md

@@ -91,6 +91,9 @@ Do not hide a missing connection string or continue startup after a migration fa
 
 The example runs migrations from the application only in development. See
 [Deploy the Database Schema](#deploy-the-database-schema) for the production approach.
+If you register additional storage instances, resolve each one with
+`IStorageInstanceSchemaFactory.GetStorageInstanceSchema(storageInstanceId, cancellationToken)` and migrate it
+separately. See [Multiple Storage Instances](/identityserver/data/providers/duende-storage/multiple-storage-instances.md).
 
 ### Configuration Stores
 

astro/src/content/docs/identityserver/data/providers/duende-storage/multiple-storage-instances.md

@@ -44,6 +44,16 @@ Selecting a second database provider for the same instance, whether in one `AddS
 throws an `InvalidOperationException`. This catches accidental double registration instead of silently replacing the
 first provider.
 
+## Choose the Schema API
+
+Use `IStorageInstanceSchema` when you need to create, upgrade, or verify the default storage instance. Resolving it
+without a key returns the schema for `StorageInstanceId.Default`.
+
+Use `IStorageInstanceSchemaFactory` when you need the schema for a specific instance. Pass the `StorageInstanceId`
+created for the named instance to `GetStorageInstanceSchema(...)`, then call the same migration and verification
+methods on the returned `IStorageInstanceSchema`. The factory does not fall back to another instance when the
+requested instance is not registered, so configuration errors fail at the point where you resolve the schema.
+
 ## Register a Second Instance
 
 Give the instance an explicit ID, register a provider for it, then map a category to it:
@@ -92,8 +102,8 @@ app.UseIdentityServer();
 app.Run();
 ```
 
-Migrate every instance you register. `IStorageInstanceSchema.MigrateAsync` resolves the default instance only;
-use `IStorageInstanceSchemaFactory.GetStorageInstanceSchema(storageInstanceId, ct)` to resolve and migrate a named
+Migrate every instance you register. `IStorageInstanceSchema.MigrateAsync` resolves the default instance only. Use
+`IStorageInstanceSchemaFactory.GetStorageInstanceSchema(storageInstanceId, ct)` to resolve and migrate each named
 instance, as shown above.
 
 ## Cross-Product Example: IdentityServer, User Management and Spaces