Just a few points to add to the excellent detail above. Many years ago when measuring VMCG on a 4 engined regional jet, we took account of tyre pressure and if I recall, the low pressure tyres which were a customer option had a lower VMCG value.
We also never disconnected the nosewheel steering. Although not used during the tests, it was thought that you might actually need it to avoid deviating on to the grass!
I also think that we published a higher VMCG for narrower runways.
While certificating a two engined business jet formerly built in North Wales, the authorities raised an eyebrow at the pilot reaction times. The almost instanteous reaction times were due to the fact that the first indication the pilot got of engine failure was the movement of the rudder pedals due to the rudder bias system.
I think we may have scheduled VMCG against crosswind when certificating to BCAR. (I might be wrong about that - it was a long time ago)