Just looking through the Labour Party’s rules, as you do. They state, in Rule, 3.3.1.B
When a Party conference is called at short notice, the secretaries of affiliated organisations and CLPs shall, on receiving the summons,instantly take steps to secure representation of their organisation in accordance with the constitution and these rules.
The special conference called to discuss the Collins Review was convened in breach of this rule, the National Office (i.e. the Compliance Unit) ruled that the delegates from the previous conference would represent the CLPs/Affiliated Organisations. I might be misunderstanding the meaning of “secure representation”, but since attendance is not mandatory, I don’t think so.