diff --git a/InterlinedList/Models/ListDataRow.cs b/InterlinedList/Models/ListDataRow.cs
index fd5b2f7..30134b5 100644
--- a/InterlinedList/Models/ListDataRow.cs
+++ b/InterlinedList/Models/ListDataRow.cs
@@ -2,15 +2,88 @@
 
 namespace InterlinedList.Models;
 
+/// <summary>
+/// One row of a list's data, from <c>GET /api/lists/{id}/data</c>.
+/// </summary>
+/// <remarks>
+/// <para>
+/// Field set reconciled against the live read payload 2026-09-16. Row keys are
+/// exactly: <c>id, rowData, version, createdAt, updatedAt, createdByUser,
+/// lastEditedByUser</c>.
+/// </para>
+/// <para>
+/// <b><see cref="ListId"/> is deliberately NOT <c>required</c>.</b> The read
+/// endpoint does not send it — declaring it required made
+/// <c>System.Text.Json</c> throw
+/// <c>"missing required properties including: 'listId'"</c>, so <i>any</i> list
+/// holding at least one row failed to load. Watch for the asymmetry that hid
+/// this: <c>POST /api/lists/{id}/data</c> <i>does</i> return <c>listId</c> in
+/// its <c>{message, data:{…}}</c> envelope; only the read path omits it. The
+/// caller already knows which list it asked for.
+/// </para>
+/// </remarks>
 public sealed class ListDataRow
 {
     public required string Id { get; init; }
-    public required string ListId { get; init; }
+
+    /// <summary>
+    /// Owning list. Absent on the read path — see the remarks. Populated when a
+    /// row comes back from a create/update response.
+    /// </summary>
+    public string? ListId { get; init; }
+
     public required Dictionary<string, JsonElement> RowData { get; init; }
+
+    /// <summary>
+    /// Monotonic row version, incremented on each edit.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// <b>This is NOT optimistic concurrency, despite looking like it.</b> An
+    /// earlier revision of this comment claimed it was; probing disproved that
+    /// (2026-09-16). Sending a deliberately stale <c>version</c> on
+    /// <c>PUT /api/lists/{id}/data/{rowId}</c> is accepted:
+    /// </para>
+    /// <code>
+    /// row at version 2, PUT with {"data":{…},"version":1}
+    ///   -> 200, version becomes 3, the write lands
+    /// </code>
+    /// <para>
+    /// So the server does not compare-and-swap on it — row writes are
+    /// last-writer-wins and a concurrent edit is silently lost. Treat this as a
+    /// display/audit value only. (Contrast the app-settings store, which DOES
+    /// do real CAS via <c>baseVersion</c> and returns <c>409
+    /// version_conflict</c> — see #41.)
+    /// </para>
+    /// </remarks>
+    public int Version { get; init; }
+
+    /// <summary>Server-assigned ordinal. Null on a schema-less list.</summary>
+    public int? RowNumber { get; init; }
+
     public DateTimeOffset CreatedAt { get; init; }
     public DateTimeOffset UpdatedAt { get; init; }
 
-    /// <summary>Read-only "key: value, key2: value2" preview — good enough since rows are freeform JSON with no schema.</summary>
+    /// <summary>Who added the row. Useful on a shared list — see the contributors work (#65).</summary>
+    public ApiUser? CreatedByUser { get; init; }
+
+    /// <summary>Who last edited it; null when never edited since creation.</summary>
+    public ApiUser? LastEditedByUser { get; init; }
+
+    /// <summary>
+    /// Read-only "key: value, key2: value2" preview. Adequate while rows are
+    /// freeform; the typed, schema-driven renderer is #21.
+    /// </summary>
+    /// <remarks>
+    /// Note for anyone writing rows: <c>PUT /api/lists/{id}/data/{rowId}</c>
+    /// <b>replaces</b> <c>rowData</c> rather than merging it. Verified live —
+    /// a row holding <c>{a,b}</c> PUT with only <c>{a}</c> came back as
+    /// <c>{a}</c>, silently dropping <c>b</c>. So an editor must re-send every
+    /// key it knows about, echoing untouched values.
+    /// </remarks>
     public string DisplaySummary =>
         string.Join(", ", RowData.Select(kv => $"{kv.Key}: {kv.Value}"));
+
+    /// <summary>Edited since creation, per <see cref="LastEditedByUser"/>.</summary>
+    public bool HasBeenEdited => LastEditedByUser is not null;
 }