It seems their rank was basically the same, except for Data's position. So it seems like Geordi didn't have to be formal with Data as far as rank.
Geordi never called Data "sir" but usually just Data, or in some cases "commander".
In some cases Geordi gave Data orders in engineering and
on the bridge.
And then, whenever the bridge is taken over or can't function, control and command of the entire ship is temporarily transferred to engineering.