Though they are not mentioned as sister ships, Coen and De Witt look like sister ships. They were built a few years apart on the same yard (Nederlandsche Scheepsbouw Mij., Amsterdam). Both had their bow reconstructed. I found a picture of Coen with the old bow and sure enough, it's like the steamer on the medal. However, the picture of De Witt above is undated. It is quite possible that the bow looked the same as on Coen before it was reconstructed.
I think there is good case for the ship on the medal being De Witt, simply because it was delivered later, so that at the time of the jubilee, it was the latest NSM ship. You would expect that on such an occasion, the company would have wanted to show their latest ship, not the penultimate one.
Peter