Re: Every user?
It is my understanding that an ISP external IPv4 address - that is visible across the internet - might be shared by many users at the same time. Most/many users don't usually need a reserved IPv4 external address. That's how the IPv4 shortage of addresses has been mitigated for many years.
The TCP/UDP connections for such users are multiplexed on one external address by user source port number translation. A user's dynamically assigned source port numbers will change quite quickly after they are deemed to have expired. They don't necessarily even have to all be on the ISP's same IPv4 external address.