diff --git a/backend/app/models/knowledge_base_document.py b/backend/app/models/knowledge_base_document.py
index e613260d..c7844329 100644
--- a/backend/app/models/knowledge_base_document.py
+++ b/backend/app/models/knowledge_base_document.py
@@ -19,7 +19,7 @@ class KnowledgeBaseDocument(Base):
     status: Mapped[str] = mapped_column(String(32), default="indexed")
     source_type: Mapped[Optional[str]] = mapped_column(String(64), nullable=True, index=True)
     authority: Mapped[Optional[str]] = mapped_column(String(255), nullable=True)
-    effective_date: Mapped[Optional[str]] = mapped_column(String(32), nullable=True)
+    effective_date: Mapped[Optional[str]] = mapped_column(String(128), nullable=True)
     region: Mapped[Optional[str]] = mapped_column(String(120), nullable=True, index=True)
     tags_json: Mapped[Optional[list[str]]] = mapped_column(JSON, nullable=True)
     content_excerpt: Mapped[Optional[str]] = mapped_column(Text, nullable=True)
diff --git a/backend/migrations/versions/20260516_0021_widen_knowledge_document_effective_date.py b/backend/migrations/versions/20260516_0021_widen_knowledge_document_effective_date.py
new file mode 100644
index 00000000..ec22e760
--- /dev/null
+++ b/backend/migrations/versions/20260516_0021_widen_knowledge_document_effective_date.py
@@ -0,0 +1,45 @@
+"""widen knowledge document effective date metadata"""
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = "20260516_0021"
+down_revision = "20260513_0020"
+branch_labels = None
+depends_on = None
+
+
+def _table_names(inspector: sa.Inspector) -> set[str]:
+    return set(inspector.get_table_names())
+
+
+def _column_by_name(inspector: sa.Inspector, table_name: str, column_name: str):
+    for column in inspector.get_columns(table_name):
+        if column["name"] == column_name:
+            return column
+    return None
+
+
+def upgrade() -> None:
+    bind = op.get_bind()
+    inspector = sa.inspect(bind)
+    if "knowledge_base_documents" not in _table_names(inspector):
+        return
+    column = _column_by_name(inspector, "knowledge_base_documents", "effective_date")
+    if column is None:
+        return
+    current_length = getattr(column["type"], "length", None)
+    if current_length is None or current_length < 128:
+        op.alter_column(
+            "knowledge_base_documents",
+            "effective_date",
+            existing_type=sa.String(length=current_length or 32),
+            type_=sa.String(length=128),
+            existing_nullable=True,
+        )
+
+
+def downgrade() -> None:
+    # Keep the wider column on downgrade so already absorbed multi-source metadata is not truncated.
+    return