Maybe it was used for some shots in later films too? Dunno.
Devastator as part of Death Squadron.SWTC has a list of differences:ISD-I
triple vectrals on primary thruster nozzles
no protruding observation nodules on command tower
main bay: 8 transverse ribs on the long walls
secondary bay: hangar on aft wall
device akin to linear array struts is mounted on command tower forward face
huge quad cannons in the minor brim trench notches
stern triangular keel plating is further astern
tower support neck meets hull with a vertical surface
main turrets: six doublet heavy turbolaser batteries; two doublet ion cannons
ISD-II
ring baffles on primary thruster nozzles
some bridge windows possibly visible on command tower
bridge panorama situated beneath thick vertical feature
main bay: 7 transverse ribs on the long walls
secondary bay: hangar on forward wall
no obvious guns in the brim trench
stern triangular keel plating is closer to ventral bulb
tower support neck meets hull with a continuous diagonal surface
main turrets: eight octet turbolaser batteries
slightly different proportions for the main hull
(the corvette is looking great btw)