Same here... but a little more clarification wouldn't hurtI think I follow what you are describing.
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If I'm interpreting correctly, the service, transformer, generator, ATS, MDP are all on a pad 150ft from building being discussed. Conductors running to said building are feeders, not service conductors. Both grounded (not required) and grounding conductors are run to a main disconnecting means at building. There would be no grounded to grounding bond at this building, but as mentioned, there must be a grounding electrode system (GES). Essentially the only difference between this GES and one where the service disconnecting means is located at a building or structure is the absence of the mentioned neutral to ground bonding.