I have a couple of opinions, and they’re worth every penny you paid for ‘em.
Where ground-fault sensing is needed, downstream neutral-ground connections will desensitize the type of ground-fault protection needed for 480Y/277V service/feeder overcurrent devices. For modern GFCIs, a neutral-ground connection should trip the upstream GFCI breaker or receptacle. {That may be the case with AFCIs, too.}
Testing for downstream neutral-ground connections can be done with gizmos intended for the purpose. Alternately—at the panelboard—branch circuits could be tested with an ohmmeter while lifting individual neutrals and checking for continuity. Also, at the receptacle a temporary hot-neutral load could be applied while looking for an at-the-plug increase in neutral-ground voltage. Too much N-G voltage may indicate an excessively long circuit. Too little voltage change may catch “cheating” though a locally shorted connection.
