diff --git a/keyserver/src/creators/update-creator.js b/keyserver/src/creators/update-creator.js
--- a/keyserver/src/creators/update-creator.js
+++ b/keyserver/src/creators/update-creator.js
@@ -10,7 +10,7 @@
 } from 'lib/shared/update-utils.js';
 import type {
   UpdateInfosRawData,
-  DeleteConditionType,
+  UpdateTypes,
 } from 'lib/shared/updates/update-spec.js';
 import { updateSpecs } from 'lib/shared/updates/update-specs.js';
 import {
@@ -27,7 +27,6 @@
   type NewUpdatesRedisMessage,
 } from 'lib/types/redis-types.js';
 import type { RawThreadInfo } from 'lib/types/thread-types.js';
-import { updateTypes } from 'lib/types/update-types-enum.js';
 import {
   type ServerUpdateInfo,
   type UpdateData,
@@ -72,7 +71,7 @@
 type DeleteCondition = {
   +userID: string,
   +target: ?string,
-  +types: DeleteConditionType,
+  +types: UpdateTypes,
 };
 
 export type ViewerInfo =
@@ -539,21 +538,13 @@
       mergedUpdates.push(updateInfo);
       continue;
     }
+    const typesOfReplacedUpdatesForMatchingKey =
+      updateSpecs[updateInfo.type].typesOfReplacedUpdatesForMatchingKey;
     const currentUpdateInfo = updateForKey.get(key);
     if (
       !currentUpdateInfo ||
-      updateInfo.type === updateTypes.DELETE_THREAD ||
-      updateInfo.type === updateTypes.JOIN_THREAD ||
-      updateInfo.type === updateTypes.DELETE_ACCOUNT ||
-      updateInfo.type === updateTypes.UPDATE_ENTRY ||
-      updateInfo.type === updateTypes.UPDATE_CURRENT_USER
-    ) {
-      updateForKey.set(key, updateInfo);
-    } else if (
-      (updateInfo.type === updateTypes.UPDATE_THREAD &&
-        currentUpdateInfo.type === updateTypes.UPDATE_THREAD_READ_STATUS) ||
-      (updateInfo.type === updateTypes.UPDATE_THREAD_READ_STATUS &&
-        currentUpdateInfo.type === updateTypes.UPDATE_THREAD_READ_STATUS)
+      typesOfReplacedUpdatesForMatchingKey === 'all_types' ||
+      typesOfReplacedUpdatesForMatchingKey?.has(currentUpdateInfo.type)
     ) {
       updateForKey.set(key, updateInfo);
     }
diff --git a/lib/shared/updates/bad-device-token-spec.js b/lib/shared/updates/bad-device-token-spec.js
--- a/lib/shared/updates/bad-device-token-spec.js
+++ b/lib/shared/updates/bad-device-token-spec.js
@@ -35,4 +35,5 @@
     };
   },
   deleteCondition: null,
+  typesOfReplacedUpdatesForMatchingKey: null,
 });
diff --git a/lib/shared/updates/delete-account-spec.js b/lib/shared/updates/delete-account-spec.js
--- a/lib/shared/updates/delete-account-spec.js
+++ b/lib/shared/updates/delete-account-spec.js
@@ -73,4 +73,5 @@
     updateTypes.DELETE_ACCOUNT,
     updateTypes.UPDATE_USER,
   ]),
+  typesOfReplacedUpdatesForMatchingKey: 'all_types',
 });
diff --git a/lib/shared/updates/delete-thread-spec.js b/lib/shared/updates/delete-thread-spec.js
--- a/lib/shared/updates/delete-thread-spec.js
+++ b/lib/shared/updates/delete-thread-spec.js
@@ -61,4 +61,5 @@
     };
   },
   deleteCondition: 'all_types',
+  typesOfReplacedUpdatesForMatchingKey: 'all_types',
 });
diff --git a/lib/shared/updates/join-thread-spec.js b/lib/shared/updates/join-thread-spec.js
--- a/lib/shared/updates/join-thread-spec.js
+++ b/lib/shared/updates/join-thread-spec.js
@@ -140,4 +140,5 @@
     };
   },
   deleteCondition: 'all_types',
+  typesOfReplacedUpdatesForMatchingKey: 'all_types',
 });
diff --git a/lib/shared/updates/update-current-user-spec.js b/lib/shared/updates/update-current-user-spec.js
--- a/lib/shared/updates/update-current-user-spec.js
+++ b/lib/shared/updates/update-current-user-spec.js
@@ -53,4 +53,5 @@
     };
   },
   deleteCondition: new Set([updateTypes.UPDATE_CURRENT_USER]),
+  typesOfReplacedUpdatesForMatchingKey: 'all_types',
 });
diff --git a/lib/shared/updates/update-entry-spec.js b/lib/shared/updates/update-entry-spec.js
--- a/lib/shared/updates/update-entry-spec.js
+++ b/lib/shared/updates/update-entry-spec.js
@@ -69,4 +69,5 @@
     };
   },
   deleteCondition: 'all_types',
+  typesOfReplacedUpdatesForMatchingKey: 'all_types',
 });
diff --git a/lib/shared/updates/update-spec.js b/lib/shared/updates/update-spec.js
--- a/lib/shared/updates/update-spec.js
+++ b/lib/shared/updates/update-spec.js
@@ -43,7 +43,7 @@
   },
 };
 
-export type DeleteConditionType = 'all_types' | $ReadOnlySet<UpdateType>;
+export type UpdateTypes = 'all_types' | $ReadOnlySet<UpdateType>;
 
 export type UpdateSpec<
   UpdateInfo: ClientUpdateInfo,
@@ -88,5 +88,6 @@
     info: RawInfo,
     params: UpdateInfoFromRawInfoParams,
   ) => ?UpdateInfo,
-  +deleteCondition: ?DeleteConditionType,
+  +deleteCondition: ?UpdateTypes,
+  +typesOfReplacedUpdatesForMatchingKey: ?UpdateTypes,
 };
diff --git a/lib/shared/updates/update-thread-read-status-spec.js b/lib/shared/updates/update-thread-read-status-spec.js
--- a/lib/shared/updates/update-thread-read-status-spec.js
+++ b/lib/shared/updates/update-thread-read-status-spec.js
@@ -69,4 +69,7 @@
     };
   },
   deleteCondition: new Set([updateTypes.UPDATE_THREAD_READ_STATUS]),
+  typesOfReplacedUpdatesForMatchingKey: new Set([
+    updateTypes.UPDATE_THREAD_READ_STATUS,
+  ]),
 });
diff --git a/lib/shared/updates/update-thread-spec.js b/lib/shared/updates/update-thread-spec.js
--- a/lib/shared/updates/update-thread-spec.js
+++ b/lib/shared/updates/update-thread-spec.js
@@ -88,4 +88,7 @@
     updateTypes.UPDATE_THREAD,
     updateTypes.UPDATE_THREAD_READ_STATUS,
   ]),
+  typesOfReplacedUpdatesForMatchingKey: new Set([
+    updateTypes.UPDATE_THREAD_READ_STATUS,
+  ]),
 });
diff --git a/lib/shared/updates/update-user-spec.js b/lib/shared/updates/update-user-spec.js
--- a/lib/shared/updates/update-user-spec.js
+++ b/lib/shared/updates/update-user-spec.js
@@ -40,4 +40,5 @@
     };
   },
   deleteCondition: new Set([updateTypes.UPDATE_USER]),
+  typesOfReplacedUpdatesForMatchingKey: null,
 });