Our VPN concentrator serves several clients from one address. Will Passbeam tell them apart?

Yes. Passbeam works out which client a request belongs to from the shared secret that matches it. Each request is signed with the secret, and only the right one matches. The source address only narrows down which secrets to try.

So one concentrator on one public address can serve as many of your clients as you like. Give each client its own VPN gateway with its own secret, and register the same public address on each. This is a normal MSP setup.

Up to 32 VPN gateways can share one address. That's a technical limit, not a licence limit. If you run a concentrator for more than 32 clients, let us know before you get there.