I think nickel plating may easily have been a production variation.
I have a '53 bike with a Campagnolo seatpost in steel, it is nickel plated, the shifter band is chrome.
Do note that the band backing plates for the levers are black, not the later chrome, my example has the slotted screws.
I have seen other steel Campagnolo posts that were chrome, though the plating was not in very good condition at all on either of them.
I would call the nickel finish on mine, fair. And this is only one example.
Torrance Ca USA