diff --git a/src/modules/cards/application/useCases/commands/UpdateNoteCardUseCase.ts b/src/modules/cards/application/useCases/commands/UpdateNoteCardUseCase.ts
index 3528d79f..f48fbfc6 100644
--- a/src/modules/cards/application/useCases/commands/UpdateNoteCardUseCase.ts
+++ b/src/modules/cards/application/useCases/commands/UpdateNoteCardUseCase.ts
@@ -95,7 +95,7 @@ export class UpdateNoteCardUseCase
         );
       }
 
-      if (!noteContent.authorId.equals(curatorId)) {
+      if (!card.curatorId.equals(curatorId)) {
         return err(
           new ValidationError('Only the author can update this note card'),
         );
@@ -110,7 +110,6 @@ export class UpdateNoteCardUseCase
       // Create new card content with updated note
       const updatedCardContentResult = CardContent.createNoteContent(
         request.note,
-        curatorId,
       );
       if (updatedCardContentResult.isErr()) {
         return err(new ValidationError(updatedCardContentResult.error.message));
diff --git a/src/modules/cards/domain/services/CardLibraryService.ts b/src/modules/cards/domain/services/CardLibraryService.ts
index 58d8da29..048c7d25 100644
--- a/src/modules/cards/domain/services/CardLibraryService.ts
+++ b/src/modules/cards/domain/services/CardLibraryService.ts
@@ -37,6 +37,14 @@ export class CardLibraryService implements DomainService {
         // Card is already in library, nothing to do
         return ok(card);
       }
+      const addToLibResult = card.addToLibrary(curatorId);
+      if (addToLibResult.isErr()) {
+        return err(
+          new CardLibraryValidationError(
+            `Failed to add card to library: ${addToLibResult.error.message}`,
+          ),
+        );
+      }
 
       // Publish card to library
       const publishResult = await this.cardPublisher.publishCardToLibrary(
@@ -52,8 +60,17 @@ export class CardLibraryService implements DomainService {
       }
 
       // Mark card as published in library
-      card.addToLibrary(curatorId);
-      card.markCardInLibraryAsPublished(curatorId, publishResult.value);
+      const markCardAsPublishedResult = card.markCardInLibraryAsPublished(
+        curatorId,
+        publishResult.value,
+      );
+      if (markCardAsPublishedResult.isErr()) {
+        return err(
+          new CardLibraryValidationError(
+            `Failed to mark card as published in library: ${markCardAsPublishedResult.error.message}`,
+          ),
+        );
+      }
 
       // Save updated card
       const saveResult = await this.cardRepository.save(card);
diff --git a/src/modules/cards/tests/application/AddCardToLibraryUseCase.test.ts b/src/modules/cards/tests/application/AddCardToLibraryUseCase.test.ts
index 43a17729..acf43311 100644
--- a/src/modules/cards/tests/application/AddCardToLibraryUseCase.test.ts
+++ b/src/modules/cards/tests/application/AddCardToLibraryUseCase.test.ts
@@ -9,6 +9,7 @@ import { CuratorId } from '../../domain/value-objects/CuratorId';
 import { CollectionBuilder } from '../utils/builders/CollectionBuilder';
 import { CardBuilder } from '../utils/builders/CardBuilder';
 import { CardTypeEnum } from '../../domain/value-objects/CardType';
+import { CARD_ERROR_MESSAGES } from '../../domain/Card';
 
 describe('AddCardToLibraryUseCase', () => {
   let useCase: AddCardToLibraryUseCase;
@@ -19,6 +20,7 @@ describe('AddCardToLibraryUseCase', () => {
   let cardLibraryService: CardLibraryService;
   let cardCollectionService: CardCollectionService;
   let curatorId: CuratorId;
+  let curatorId2: CuratorId;
 
   beforeEach(() => {
     cardRepository = new InMemoryCardRepository();
@@ -44,6 +46,7 @@ describe('AddCardToLibraryUseCase', () => {
     );
 
     curatorId = CuratorId.create('did:plc:testcurator').unwrap();
+    curatorId2 = CuratorId.create('did:plc:testcurator2').unwrap();
   });
 
   afterEach(() => {
@@ -65,11 +68,18 @@ describe('AddCardToLibraryUseCase', () => {
         throw new Error(`Failed to create card: ${card.message}`);
       }
 
+      const addToLibResult = card.addToLibrary(curatorId);
+      if (addToLibResult.isErr()) {
+        throw new Error(
+          `Failed to add card to library: ${addToLibResult.error.message}`,
+        );
+      }
+
       await cardRepository.save(card);
 
       const request = {
         cardId: card.cardId.getStringValue(),
-        curatorId: curatorId.value,
+        curatorId: curatorId2.value,
       };
 
       const result = await useCase.execute(request);
@@ -79,7 +89,7 @@ describe('AddCardToLibraryUseCase', () => {
       }
       expect(result.isErr()).toBe(true);
       expect(result.error.message).toContain(
-        'URL cards can only be in one library',
+        CARD_ERROR_MESSAGES.URL_CARD_SINGLE_LIBRARY_ONLY,
       );
     });