For Communication Safety, the new joined members, including external members, will not be able to see the previous chat contents.
When it comes to practical use, group chats are convenient since you can always add new people into the chat room. However, every time when you add new people into the chat room, to filter what contents the new joined can or cannot see can be quite troublesome.
As a result, in case of information leaks in TEAM+, all the new joined people cannot see the previous contents in a chat room.
※ However, the new joined members can view the albums created before.