diff --git a/agenda/add_new_conference.py b/agenda/add_new_conference.py
index 1a6820f..e74455c 100644
--- a/agenda/add_new_conference.py
+++ b/agenda/add_new_conference.py
@@ -502,6 +502,42 @@ def parse_yaml_datetime(value: typing.Any) -> datetime | None:
     return None
 
 
+def parse_yaml_date_value(value: typing.Any) -> date | datetime | None:
+    """Convert YAML date/datetime strings to date-like values."""
+    if isinstance(value, datetime):
+        return value
+
+    if isinstance(value, date):
+        return value
+
+    if not isinstance(value, str):
+        return None
+
+    try:
+        if " " in value or "T" in value:
+            return datetime.fromisoformat(value)
+        return date.fromisoformat(value)
+    except ValueError:
+        return None
+
+
+def normalize_date_values(conf: dict[str, typing.Any]) -> None:
+    """Normalize quoted ISO date/datetime values produced by the LLM."""
+    dates = conf.get("dates")
+    if isinstance(dates, dict):
+        for field in ("start", "end", "earliest", "latest"):
+            if field in dates:
+                parsed = parse_yaml_date_value(dates[field])
+                if parsed is not None:
+                    dates[field] = parsed
+
+    for field in ("start", "end"):
+        if field in conf:
+            parsed = parse_yaml_date_value(conf[field])
+            if parsed is not None:
+                conf[field] = parsed
+
+
 def same_type_as_start(
     start_value: typing.Any,
     new_dt: datetime,
@@ -529,6 +565,7 @@ def same_type_as_start(
 
 def normalize_dates_field(conf: dict[str, typing.Any]) -> None:
     """Move legacy top-level date fields into the nested dates mapping."""
+    normalize_date_values(conf)
     raw_dates = conf.get("dates")
     dates = raw_dates if isinstance(raw_dates, dict) else None
 
@@ -550,6 +587,20 @@ def normalize_dates_field(conf: dict[str, typing.Any]) -> None:
     conf.pop("start", None)
     conf.pop("end", None)
     conf.pop("date_status", None)
+    normalize_date_values(conf)
+
+
+def validate_generated_conference(conf: dict[str, typing.Any]) -> None:
+    """Validate generated conference YAML before inserting it."""
+    try:
+        conference_date_fields(conf)
+    except ValueError as exc:
+        generated_yaml = yaml.dump(conf, sort_keys=False, allow_unicode=True).strip()
+        raise ValueError(
+            "Generated conference YAML is missing valid date information. "
+            "Expected nested `dates:` with exact/tentative start/end or "
+            f"approximate earliest/latest.\n\nGenerated YAML:\n{generated_yaml}"
+        ) from exc
 
 
 def maybe_extract_explicit_end_time(source_text: str) -> int | None:
@@ -661,6 +712,7 @@ def add_new_conference(url: str, yaml_path: str) -> bool:
     normalize_dates_field(new_conf)
     normalise_end_field(new_conf, source_text)
     normalize_dates_field(new_conf)
+    validate_generated_conference(new_conf)
 
     if detected_coordinates is not None:
         new_conf["latitude"] = detected_coordinates[0]
diff --git a/templates/conference_series_list.html b/templates/conference_series_list.html
index a39890d..f9ccc5f 100644
--- a/templates/conference_series_list.html
+++ b/templates/conference_series_list.html
@@ -21,6 +21,9 @@
       <tr>
         <td>
           <a href="{{ url_for('conference_series_page', series_id=item.id) }}">{{ item.name }}</a>
+          {% if item.attended %}
+            <span class="badge text-bg-success ms-1">attended</span>
+          {% endif %}
           {% if item.url %}
             <a class="text-muted ms-1 text-decoration-none" href="{{ item.url }}">↗</a>
           {% endif %}
diff --git a/tests/test_add_new_conference.py b/tests/test_add_new_conference.py
index 34f80d0..02d19df 100644
--- a/tests/test_add_new_conference.py
+++ b/tests/test_add_new_conference.py
@@ -145,6 +145,35 @@ def test_normalize_dates_field_moves_legacy_dates() -> None:
     }
 
 
+def test_normalize_dates_field_parses_quoted_dates() -> None:
+    """Quoted ISO dates from generated YAML should become date objects."""
+    conf: dict[str, typing.Any] = {
+        "name": "Git Merge",
+        "dates": {
+            "status": "exact",
+            "start": "2026-09-16",
+            "end": "2026-09-17",
+        },
+    }
+
+    add_new_conference.normalize_dates_field(conf)
+
+    assert conf["dates"]["start"] == date(2026, 9, 16)
+    assert conf["dates"]["end"] == date(2026, 9, 17)
+
+
+def test_validate_generated_conference_reports_missing_dates() -> None:
+    """Missing generated dates should raise a clear importer error."""
+    conf: dict[str, typing.Any] = {
+        "name": "Git Merge",
+        "topic": "Git",
+        "location": "TBC",
+    }
+
+    with pytest.raises(ValueError, match="missing valid date information"):
+        add_new_conference.validate_generated_conference(conf)
+
+
 def test_build_prompt_includes_nested_dates_and_series() -> None:
     """The prompt should describe nested dates and known series IDs."""
     prompt = add_new_conference.build_prompt(
diff --git a/tests/test_conference_list.py b/tests/test_conference_list.py
index bd68c0d..6eb26f7 100644
--- a/tests/test_conference_list.py
+++ b/tests/test_conference_list.py
@@ -118,5 +118,6 @@ def test_conference_series_pages(tmp_path: typing.Any, monkeypatch: typing.Any)
 
     assert index_response.status_code == 200
     assert b"PyCascades" in index_response.data
+    assert b"attended" in index_response.data
     assert detail_response.status_code == 200
     assert b"trip: Seattle Python trip" in detail_response.data
diff --git a/web_view.py b/web_view.py
index 534fb2b..de824e0 100755
--- a/web_view.py
+++ b/web_view.py
@@ -413,12 +413,14 @@ def build_conference_series_list() -> list[StrDict]:
         next_conf = next(
             (conf for conf in linked if conf["latest_date"] >= date.today()), None
         )
+        attended = any(conf.get("going") or conf.get("linked_trip") for conf in linked)
         item: StrDict = {
             "id": series_id,
             **series,
             "count": len(linked),
             "latest": latest,
             "next_conf": next_conf,
+            "attended": attended,
         }
         series_items.append(item)