The utility fault contribution can change at any time without any notice. A label printed today could be useless tomorrow and we wouldn't know

Most companies will know when they have lost their utility power.

A transformer change at a utility substation will not really affect the fault current at a customer purchasing power at secondary voltages like 480Y/277.
Most customers will experience their 'worst' arc flash values when they are on generator power. Less available fault current means protective devices do not enter the Instantaneous range.

We ran multiple scenarios for arc flash and typically reported the highest incident energy results regardless which scenario caused it..
At the least we ran infinite bus utility, normal reported fault current with all motors on, normal fault current with all motors off, and generator power.
Once data has been entered into a software package running multiple scenarios is not a large expense. I think my record was 15 scenarios.