This topic reminds me of the patterning thread in some ways.

The convergence of a production gun is done by dimensional control of what the maker developed and validated on a prototype just as virtually all chokes in production guns are machined to dimensional specification rather than individually tested and developed.

The maker chose the load for convergence testing and also chose the shooter(s), whose individual physical characteristics can affect POI. Even the H&H video showed an employee shooting for POI rather than the customer of the bespoke gun. It must work out well a high percentage of the time or they'd do it differently. But there was a recent post about a bespoke gun that hit off target by enough to perturb the customer.