The convertible option returned to Corvette for the 1986 model year.  For the 1986-1988 convertibles a collapsible soft top with a plastic rear window was the only option.  However starting in the 1989 model year,  a removable hard top became an option in addition to the standard soft top applied to all convertibles.  The video linked below explains these hardtops in further detail, and reviews how the hard tops were physically attached to the convertible cars.