Topics created before July 2024 don't have createdBy or createdAt stored in the Evolver state. In ExportToNebulaCommand::extractMembersFromEvents(), the creator is only added to the members list when $createdBy is truthy:
$createdBy = $topicState['createdBy'] ?? null; // null for pre-July-2024 topics
// Add creator as owner (always active)