diff --git a/search/classes/manager.php b/search/classes/manager.php
index bbb81080e81..fd25afa2cf7 100644
--- a/search/classes/manager.php
+++ b/search/classes/manager.php
@@ -1289,15 +1289,8 @@ class manager {
                 if ($batches !== $numdocs + $numdocsignored) {
                     $batchinfo = ' (' . $batches . ' batch' . ($batches === 1 ? '' : 'es') . ')';
                 }
-            } else if (count($result) === 5) {
-                // Backward compatibility for engines that don't return a batch count.
-                [$numrecords, $numdocs, $numdocsignored, $lastindexeddoc, $partial] = $result;
-                // Deprecated since Moodle 3.10 MDL-68690.
-                // TODO: MDL-68776 This will be deleted in Moodle 4.2.
-                debugging('engine::add_documents() should return $batches (5-value return is deprecated)',
-                        DEBUG_DEVELOPER);
             } else {
-                throw new coding_exception('engine::add_documents() should return $partial (4-value return is deprecated)');
+                throw new \coding_exception('engine::add_documents() should return 6 values');
             }
 
             if ($numdocs > 0) {
@@ -1454,19 +1447,8 @@ class manager {
                 if ($batches !== $numdocs + $numdocsignored) {
                     $batchinfo = ' (' . $batches . ' batch' . ($batches === 1 ? '' : 'es') . ')';
                 }
-            } else if (count($result) === 5) {
-                // Backward compatibility for engines that don't return a batch count.
-                [$numrecords, $numdocs, $numdocsignored, $lastindexeddoc, $partial] = $result;
-                // Deprecated since Moodle 3.10 MDL-68690.
-                // TODO: MDL-68776 This will be deleted in Moodle 4.2 (as should the below bit).
-                debugging('engine::add_documents() should return $batches (5-value return is deprecated)',
-                        DEBUG_DEVELOPER);
             } else {
-                // Backward compatibility for engines that don't support partial adding.
-                list($numrecords, $numdocs, $numdocsignored, $lastindexeddoc) = $result;
-                debugging('engine::add_documents() should return $partial (4-value return is deprecated)',
-                        DEBUG_DEVELOPER);
-                $partial = false;
+                throw new \coding_exception('engine::add_documents() should return 6 values');
             }
 
             if ($numdocs > 0) {
diff --git a/search/upgrade.txt b/search/upgrade.txt
index d7037ad1856..27b9451e800 100644
--- a/search/upgrade.txt
+++ b/search/upgrade.txt
@@ -1,6 +1,11 @@
 This files describes API changes in /search/*,
 information provided here is intended especially for developers.
 
+=== 4.2 ===
+
+* Support for optional final element returned by engine `add_documents()` implementations is now removed, all
+  six expected returned array elements must be present
+
 === 3.10 ===
 
 * Search indexing now supports sending multiple documents to the server in a batch. This is implemented