An interstage coverplate assembly is provided for a rotor assembly. The coverplate assembly includes an annular first coverplate, an annular second coverplate and an annular coverplate lock that extends axially between and rotatably connects the first and the second coverplates. The first coverplate includes a plurality of coverplate tabs arranged circumferentially around an axial centerline. The coverplate lock includes a plurality of lock tabs arranged circumferentially around the centerline. A first of the lock tabs circumferentially engages a first of the coverplate tabs.