The form for joining the association used to ask for your agency, your rank, your badge number, your service dates and a photograph — before it had told you a single thing about what you were joining.
It now asks four things: your surname, your first name, an email address and a country. All four are required, because they are what the association needs to write to you and to file your application. Nothing else is asked at that moment.
Everything else — your service record, your address, the photograph for your membership card — you fill in afterwards, in your own account, in whatever order and at whatever pace suits you. None of it is required. A member who never fills any of it in is still a member.