The Devastator never had more lights added to it. It does show up a lot in ESB. The scene in question shows the Devastator from a side view, flipped horizontally (so that the port side with guns becomes the starboard side with guns) with window lights added in post to match the Avanger (see photo below). My guess is that it was probably used in this scene because the 8-footer was either not finished, or was being prepped for a different shot. Either way, the Devastator was used to keep production moving.
Devastator can also be seen a few times as the fleet of destroyers approaches Hoth. In the scene where the destroyer approaches Hoth to engage its "first catch of the day," it is actually the 4-footer from the back. When the ion canon fires shots and hits it, the view from the front of the same ship is the 8-footer.
There was a smaller, 1-foot destroyer model made with fiber optics for Empire that was used only for background shots of ships far away or with the command ship.