I just realised we have created a camel case table for external identifiers - I think we should change that while we can because I think the case will trip us up in future
- see how the table name is declared as 'External_Identifiers' rather than a more consistent civicrm_external_identifiers or wmf_external_identifiers
'External_Identifiers' => [
'group' => [
'extends' => 'Contact',
'name' => 'External_Identifiers',
'table_name' => 'External_Identifiers',