Does that include group chats with history (i.e. add a new member and they see the previous discussion)? I'm curious how the encryption would work in that case

Does that include group chats with history (i.e. add a new member and they see the previous discussion)? I'm curious how the encryption would work in that case. In the simplest case I suppose the invite could contain a shared key, but is there an individually-keyed approach?