One organisation, many hulls.
Your firm holds the account; every vessel you act for sits in the same fleet, with its own applications, documents and expiries.

Brokers, agents and managers
Run every owner's applications from one organisation. Each hull records its registered owners; every message and document stays on the file it belongs to.
How it fits together
Two different things, kept apart on purpose — because a register that recorded whoever typed the application would be recording the wrong person.
Your firm holds the account; every vessel you act for sits in the same fleet, with its own applications, documents and expiries.
Ownership is recorded against the hull in shares, and an owner recorded there need never have signed in. The register says who owns the vessel, not who filed the paperwork.
A document a registry approved for a vessel is offered back the next time that vessel needs it. Your firm's own papers go on file once and attach themselves when a new checklist is issued.
Invite them and they see the same fleet and applications the moment they accept. Roles decide who can act, and every action is recorded against the person who took it.
And still
Acting for an owner does not change who makes the decision. A registrar accepts, asks for more, or declines — and the reason is on the file, where the owner you act for can read it too.
Start today
Create the account, add a vessel, and see what a registry's checklist looks like when nobody has retyped it.